IIRC, Fatman was to be painted a 'mustard' color. If someone has the original kit with the instructions, they should be able to tell you what color Monogram tells you to paint the little boy. There are no markings on the bomb of any kind (that I can discern), on black and white photos or the color photo at the USAF museum.
The black and white photos of another similar bomb show it to be a color that is not black. A sister bomb to 'Little Boy' in the museum of the air force is painted in, what is to me, a semi-gloss olive drab.
