For some clients, SMP chat appears to be white now. I am an admin who was afflicted by this bug in 1.1 Minecraft patch. After a search, it seems that Intel's and other integrated graphics chips are now no longer supported by Minecraft to have colored chat.

I will try to find a mod or a fix for this, and will update. Meanwhile, know that you do not have an isolated case and that it is not the server's problem.