Most paint stores have a laser-matching device, which can match colors from any source to standard house paint. Use an HO model, or a magazine photo, or a photo downloaded from the web, and printed on a good color printer. Just a suggestion: paint a "separator stripe" in white, to go between the black and the green. Cover it with about 1" masking tape. This will keep the line between the other two colors clean, and represent the long hoods of the rebuilt "whiteface" locos.
You can also do a yellow stripe/black pinstripe for the Santa Fe scheme of silver and red. Again, check pix of the locos on the web and in magazines like TRAINS and Model Railroader.