If you want something that is blue and won't wash out, get the t5 blue plus bulb. I have that one in the closet, it is nice for what it is, but it is a bit blue for my taste, personally. It would make a nice halide supplement blue, but as after-hours lighting it isn't my favorite.
For my t5s I run 2 x 24w: 1 aquablue special + 1 actinic 03. They are washed out by the 250w halide which is the 14k Ushio running on the HQI ballast, though. But, I'm actually quite pleased. It is nice and bright in the daytime. The Ushio runs very white, the tank looks like a real reef- super bright! Then, when the halides are off, the t5s are amazingly beautiful, it is the most lovely ambiance lighting I've ever had. I cannot, truly cannot, be more pleased about the bulb combo.
What ballast do you have? Is it HQI, or normal magnetic ballast, or is it an e-ballast?
-A