i ahte it when no one answers the posts, il help.
well for a start RDs do change their colour as they grow, beware they grow fast, i got 3 -2"ers a month ago and the largest one is aprouching 4" now, the colour varys greatly but i have yet to see a yellow one

when igot my three i got one with a VERY intense red on his face and white udnerbelly, one orange and one white and orange, mind you there was some with black on them their and i nearly got one, i wouldnt worry im sure its just his colour pattern and hel look great when hes an adult. i dont know how long you ahve had your green terror but the males ones grow faster then bamboo! ive got a 8" male ive only had about 2.5 months since i got him at 1" lol.
my red devils can be nippy towards eachover but are friendly with the other tankmates, well for the moment, as im moving them when they are grown on, but the same goes for my green terror, mildly teritorial but hasnt acused any damage to anything. keep them in there with eachover, feed the devil more than the terror or the green terror will pick on the devil as he gets bigger, if you feed them alternating amounts u can get them around the similar size. keep an eye on them incase any fighting does ocur, and good luck mate, if you need any more info or wanne ask me sumit jst pm me,
regards kubora666