Well first, what type of fixture do you have? Obviously a 6 bulb t5 setup, but what brand, what type of reflectors, how deep is the tank, etc?
I used ATI brand bulbs w/SLR reflectors over my 40b and my green toad had awesome color. This pic is like the week i got my toadstool, and apparently i didnt take any more pics after that to show a comparison, but it turned even more green than this pic after about 3 months or so, and the colors popped a lot more after a while, and the base turned a lot more purple, rather than that brownish/yellow base that shows in this pic.
However, now i've got that same coral under the exact same bulbs (actually 2 more bulbs...i got a 6 bulb fixture now, with the same exact bulbs) about the same height in the tank, and its lost lots of color. I'd say its more of a yellowish green now, not that nice metalic green it was before. My fixture now is the nova extreme, and even though there's 2 more bulbs, it doesnt light up nearly as well as the other w/the SLR reflectors
So basically, i'm trying to show proof that with t5's, you need to make sure you've got the right reflectors...otherwise they arent so great. Unfortunately, i dont have the comparison picture of what it looks like now under the new fixture, but i'll work on getting that up in the next day or so.