Being a TC, it most likely not the fuse, but thought I would add that just in case.

Some HID kits tend lose color quickly. I know Xentec HID Kits lose their color quickly. I had tons of problems from them back when I was selling. I had a guy send me some just a month ago for warranty that he bought 10 months ago. He had a Bi-Xenon kit in 6000k and one of them turn yellow like 4300k.