Mark -
All of your stats look good. I would have to guess that it is your lighting that has changed the coloration. That being said:
I have a nice tricolor valida colony that I started from a 2" frag about 6 months ago. The colony is now larger than a baseball. It has kept its coloration beautifully.
I managed to break a small 1" piece off of it after I had it for about a month. This new piece is all green, and has encrusted the rock I glued it on heavily. Just this month, one of the branches started to turn ice blue toward the tip, and it is finally starting to resemble the parent colony.
My tank is lit bit T5's, and my water parameters are very similar to yours.