USN WW2 colors were specified in the manual Ships-2. There were 3 revisions to the original release, check this website sponsored by Snyder and Short Enterprises for a wealth of detailed information: www.shipcamouflage.com/warship_camouflage.htm. The manual describes various paint and camouflage schemes, or "measures". As the war went on, these changed based on experience and theater.

The dates of the wartime SHIPS-2 releases, and Elco PT boats completed the month of release were:
January 1941 - Initial release
December 1940 boats completed PT 15-19, break in production until the 77' designed PT 20-28 were completed June 1941.
September 1941 - Revision 1
September 1941 boats completed PT 45-48.
June 1942 - Revision 2
June 1942 boats completed PT 103-106, new 80' design.
March 1943 - Revision 2 supplement
March 1943 boats completed PT 194-195.

PT boat colors and camouflage can be confusing with all the measures, changes, paint sources, and rarity or fading of color images. Paint could be pre-mixed or field mixed from formulas. Some PT boats were painted shades of green to match island vegetation.

From what I've been able to dig up, a 1942 103 series boat would have first been painted
Dark Gray 5-D on the deck and topsides
Navy Gray #5 on the hull
And Copperoid on the bottom

PT boats in the Pacific patrolled often at night. I was wondering about how effective camouflage was in the dark, this is from Ships-2 Revision 2:

Measures for reducing visibility have best chance of success at night, in gray weather or on hazy days when visibility is limited. Very light colored ships are best at night except in the glare of searchlight. Light colored ships are best against periscope observation and dark ships are best against air observation. When light ships are clearly visible it is easy to judge target angle and make identification. Dark ships are much better in this respect.

A nighttime problem the crews faced was the bioluminescence of their wake when running along at anything except idle that no camouflage could hide. To quote the captain of the 105, Dick Keresey:

"At night in the tropics, our wake, which was large for such a small boat, glowed madly from bioluminescence. Millions of microscopic organisms disturbed by the thrashing of propellers turned on their lights to see what was going on. Looking down over the stern, I was fascinated by the way those tiny lights swirled up and down, then not amused at all when I saw that at any speed above idling that wake was a long, shining arrow pointing right up our a**".

Other informative websites:
http://www.researcheratlarge.com/Ships/S19-7/index.html, Many Ships-2 update memos and instructions.
http://www.hnsa.org/doc/camo/index.htm, Ships-2 Revision 2
http://home.att.net/~shipmodelfaq/smf-q046.html, Contributed by Jon Warneke.
http://www.steelnavy.com/usnchips.htm, Similar to above with different color chips.
http://www.uscg.mil/history/regulations/Cutter_Painting_Regs_Index.asp, Coast Guard 1935 instructions for painting. Color chip link: http://www.uscg.mil/history/gifs/USCG_1935_Color_Chips.jpg

The color samples found below include the Munsell and RGB equivalents where known. The RGB values, as well as the values used by this pages html code, were derived from Photoshop and the Munsell Conversion Software that has a 1931 value selection. The site states the program is free until 2009. I didn't know if 1931 was the right edition but John Snyder of Snyder And Short Enterprises and White Ensign Models helped me out:

I can confirm that the 1931 Munsell Book of Color is an appropriate edition for you to use for USN WW2 paints. The USN based their colors on the 1929 Munsell Book of Color, and its updates through 1942.

Beginning in 1944 Munsell began revising their color notation system, finally finishing about 1965. This resulted in the current Munsell Book of Color, and there is no correlation between the color notations in the current book and the original edition.

The samples are the nearest match I can manage and meant to give a general idea of the color. For best results use good model paint. A good model paint has finer ground particles so it will cover as thinly as possible. From what I've read one of the most accurate is the line made by White Ensign and available in the US through Snyder And Short Enterprises at shipcamouflage.com. Please let me know if you find any errors or if you have additional values or information to contribute.

Except for my color conversions most of the color information found below is from a Plastic Ship Modeler Magazine article (issue #97/3) by Alan Raven reprinted at shipcamouflage.com. Notes found in the color sample area are from this article. Excellent work Alan!

Color, Year	Number	Munsell value, RGB value On color sample background with notes from Allen Raven's article where applicable. If needed, highlight text to see it against light colored backgrounds.
Navy Gray, 1919	#5	10B 6.5/1.5, 151 162 169
Deck Gray, 1919	#20	N 3.6/0, 87 87 87 :: #20 Deck Gray (1919) should not be confused with #4 Deck Gray 20 (1944). Although both were of neutral tone (i.e. a nice black and white only), #4 Deck Gray 20 (1944) was darker.
Black, 1920's	#82 and #24	N 2.5/0, 62 62 62
Light Gray, 1941	5-L	10B 7/1.5, 165 175 182 :: 5-L (1941) should not be confused with 5-L (1943), the two colors being quite different. 5-L (1943) was first used on Measures 23 and 31. 037 Light Gray 5-L was a neutral gray (i.e. without hue) introduced in very late 1944.
Ocean Gray, 1941	5-O	5PB 4.5/3, 100 109 129 :: Same tint as 1942 Flight Deck Stain #21.
Dark Gray, 1941	5-D	5PB 2/1.5, 49 52 62
Haze Gray, 1941	5-H	5PB 5.7/1.6, 135 140 149
Haze Green, 1941	-	7G 5.9/2.5, 120 152 137
Sea Blue, 1941	5-S	2.5PB 3.6/4, 66 89 114
Haze (Cabot), 1941	-	7PB 3.2/2, 75 77 93
Pearl Harbor Blue, 1941	3 test colors	7.5PB 1.5/6, 38 39 78
Sapphire Blue, 1941	-	5PB 2.2/6, 31 56 94
PT Green, 1941	-	Unknown, locally obtained? Documentary and photographic evidence strongly suggest a green of medium tone.
Cavite Blue, 1941	-	5PB 4/2, 91 97 111 ***?5PB 3/2?, #434A58, 67 74 88***
Union Castle Lavender, 1941	-	10P (P-RP) 6/4, 166 139 160
Navy Blue, 1941	5-N, same as 1944 5-NB Navy Blue	5PB 3/2, 67 74 88
Thayer Blue, 19?	5-B	5PB 6.5/2, 154 161 172
Deck Blue, 1942	20-B	5PB 3/1.5, 69 74 84
Deck Blue Revised, 1942	20-B	5PB 3/4, 59 74 101
Blue Flight Deck Stain, 1942	250N	5PB 3/1.8, 68 74 86
Flight Deck Stain, 1942	#21	5PB 4.5/3, 100 109 129 :: Same tint as 1941 Ocean Gray 5-O.
Flight Deck Stain Revised, 1942	#21	5PB 3/4, 59 74 101 :: #21 Flight Deck stain (1944), although different from the 1943 #21 stain, did not have the word "revised" as part of the title on the official camouflage sheets. The suffix was added by the author to distinguish between the two stains.
Mountbatten Pink (Dark), 1942	-	5RP 5/1.5, 131 118 122
Elco Gray, 1942	-	Exact color and tone unknown. Worn by several PT Boats upon arrival in the Pacific theatre in 1942. Elco Gray was a PT Boat crew term and the color may have been "Ocean Gray". Elco Gray was used by PT Boat squadrons 2 and 3 at the start of the Solomons campaign.
Light Gray Green, 1942	-	Exact color and tone unknown. Used from late 1942 by PT 61 and possibly other boats of Squadron 3.
Countershade Gray, 1942	-	Exact color and tone unknown. Described by Elco who originated the color, as a blue very similar in color to Thayer Blue and Western Approaches Blue, but slightly darker in tone.
Yellow Green, 1942	-	Exact color and tone unknown. Described by Elco who originated the color as a light yellow green.
Medium Pink, 1942	-	Exact color and tone unknown. No color sample or formula found. This color may have been based upon the pink that was believed to have been worn by some British corvettes in the 1941/42 period. Not to be confused with Mountbatten Pink, a quite different color.
Mauve, 1942	-	Evidence suggests that this color could be Mountbatten Pink.
Green, 1942	-	Evidence suggests that this color could be Western Approaches Green.
Blue, 1942	-	Evidence suggests that this color could be Thayer Blue.
Brown, 1942	1A	5YR (YR-Y) 2/2, 65 49 41
Brown, 1942	2A	5YR (YR) 3/4, 99 66 46
Brown, 1942	3A	10YR (YR-Y) 3.5/3, 102 81 57
Brown, 1942	4A	10YR (YR-Y) 5/6, 154 115 57
Green, 1942	1A	5GY (GY) 3/2, 70 76 59
Green, 1942	2A	5GY (GY) 3.5/4, 77 90 50
Green, 1942	3A	5G 4.5/2, 93 114 103
Green, 1942	4A	5GY (GY) 4/6, 84 104 37
(Green), 1942	5/84 - 2/5TMA	5G 5/8, 10 139 98 :: Same as 1943 MTB Green?
(Blue Green), 1942	5/84 - 4/5TMA	5BG 4/4, 53 105 102
Lime Green, 1942	-	Exact color and tone unknown. Known to be light in tone and used by APD's and landing craft from mid 1942 into 1943. The color was usually used as the field or background color, over which was painted streaks of dark green.
Pale Gray, 1942	5-P	5PB 8/1, 197 201 206
Light Gray Revised, 1943	5-L	5PB 7/2, 167 174 185 :: 5-L (1941) should not be confused with 5-L (1943), the two colors being quite different. 5-L (1943) was first used on Measures 23 and 31. 037 Light Gray 5-L was a neutral gray (i.e. without hue) introduced in very late 1944.
Dark Green, 1943	Formula 759	Exact color and tone unknown. It may be the color "Green IA" (1942 series), or it could be the Dark Green of 5/84 - 4/5TMA. It should be noted that "Green 1A" and "5/84 - 4/5TMA" are quite different in hue.
MTB Green, 1943	-	5G 5/8, 10 139 98 :: There is the possibility that this color was the one used on PT Boats upon transfer to the British under lease lend, and never used on American Flag Boats. Same as 1942 Green?
Robins Egg Blue, 1943	-	Exact color and tone unknown. Known to be very light in tone. There is the possibility that Robins Egg Blue is in fact Thayer Blue.
Haze Green, 1943	5-HG	10GY (GY-G) 6/2, 134 152 132
Ocean Green, 1943	5-OG	10GY (GY-G) 5/2, 110 126 109
Navy Green, 1943	5-NG	10GY (GY-G) 3/2, 64 77 64
Deck Green, 1943	20-G	10GY (GY-G) 2/2, 45 55 46
Pale Green, 1943	5-PG	5GY 8/2, 197 204 172
Light Green, 1943	5-LG	5GY 7/2, 170 177 148
Haze Green Revised, 1943	5-HG	5GY 6/2, 143 150 124
Ocean Green Revised, 1943	5-OG	5GY 5/2, 117 124 102
Navy Green Revised, 1943	5-NG	5GY 3/2, 70 76 59
Green Tinting Medium, 1944	5-GTM	5GY 3.5/3, 79 89 59
Green, 1944	#1	5GY 5.5/3, 128 139 103 :: Officially described as Outside Green 1 but usually referred to on camouflage sheets as simply #1 Green. This color should not be confused with the 1942 color known as Green 1A.
Green, 1944	#2	5GY 4/2, 93 99 79 :: Officially described as Outside Green 2 but usually referred to on camouflage sheets as simply #2 Green. This color should not be confused with the 1942 color known as Green 2A.
Green, 1944	#3	5GY 2.5/2, 59 65 50 :: Officially described as Outside Green 3 but usually referred to on camouflage sheets as simply #3 Green. This color should not be confused with the 1942 color known as Green 3A.
Brown, 1944	#4	10YR (YR-Y) 4/3, 115 93 67 :: Officially described as Outside Brown #4, but usually referred to on the camouflage sheets as simply #4 Brown. This should not be confused with the 1942 color known as Brown 4A.
Outside Gray, 1944	#46	N 8/0, 200 200 200
Light Gray, 1944	#37 5-L	N 7/0, 173 173 173 :: 5-L (1941) should not be confused with 5-L (1943), the two colors being quite different. 5-L (1943) was first used on Measures 23 and 31. 037 Light Gray 5-L was a neutral gray (i.e. without hue) introduced in very late 1944.
Haze Gray, 1944	#27 5-H	N 6/0, 147 147 147
Ocean Gray, 1944	#17 5-O	N 5/0, 122 122 122
Medium Gray, 1944	#16	N 4.9/0, 119 119 119
Outside Gray Revised, 1944	#11	N 4/0, 97 97 97
Navy Gray, 1944	#7 5-N	N 3.4/0, 83 83 83
Deck Gray, 1944	#4 20	N 2/0, 52 52 52 :: #20 Deck Gray (1919) should not be confused with 04 Deck Gray 20 (1944). Although both were of neutral tone (i.e. a nice black and white only), #4 Deck Gray 20 (1944) was darker.
Navy Blue, 1944	5-NB, same as 1941 5-N Navy Blue	5PB 3/2, 67 74 88

The following is a guess.

Color, Year	Number	Munsell value, RGB value
Coperoyd	Company trade name	Unknown, color is a guess

Note the paint wear on the next two images, when I first saw the stern shot I thought the deck was awash. The 2nd image is from around the front turret of the 149:

Here is the paint section from the Navy PT boat build manual found at http://www.hnsa.org/doc/pt/specs/index.htm . Please note that this manual is a later version than the 103 class, read coverage notes below the title: