Which version of Lazarus? Snapshot (if so which date) or "normal" (0.9.10 or 0.9.129?
Compiling for Gtk, Gtk2, Gnome?
Works for me on Windows, let me test on Linux.
My Linux (Ubuntu 5.10) runs Lazarus 0.9.11 beta from 4-11-05. If I change TForm.Color, it doesn't really change, that's correct. I'm going to update to a current snapshot and will test again.