I wish I had a tank with some dark gravel I think the lighter sand coloration may be causing them to stay a bit on the light side you know oh well though see what they look like in a month or two..
heres a pic of mine i think hes a male, but the water is kind of dark in the pic and he still a bit shy hes about 6-7in and is still healing from when i rescued him he was being kept in big tank with super aggressive cichlids like red devils, etc at the lfs, but yeah so hes not all the way healed up yet but is still showing some great color, he actually has even more blue than this and shows it on the top half of his body as well but he was already unhappy with the camera flash in these pics lol. when i first got him i wouldnt even been able to ID as robertsoni unless fellow MFKer told me about him, he was showing no color at all n was all pale with dark stripes the poor thing, to OP yours look great though cant wait to see what they look like a couple inches bigger