Mine changes depending on his mood. When he was with other tangs and wanted to keep a low profile he darkened his colors so he wouldn't stand out (wasn't stressed or bullied, swimming and eating fine, just stayed dark). After removing the other fish his colors have gone a little back to what he should be, so I'll say the colors could be pretty variable depending on the fish (LOL, for a while there it looked like I had a cheap black tang).