I have the same problem using ubuntu 6.10 & the latest Beryl/XGL. I believe I submitted a bug report about this problem a while back.

With more and more Linux users using AIGLX/XGL & Compiz/Beryl, Xara devs should really look into this problem. I have not seen any other application with a color picker have this problem. Gimp, Inkscape, Scribus, Gcolor2, etc... All have color pickers that work just fine with compiz/beryl & XGL/AIGLX.

While waiting for this issue to be fixed, I have been using Gcolor2 as my picker and manually pasting the color values into xtreme. It's very inconvenient, but it allows me to continue using xtreme without sacrificing the benefits of a hardware accelerated desktop.