When you say 8bit, do you mean a Depth of 8? That is very unusually low. I'm set on 24, 32 is pretty standard also, 1 would be for that old C64 monitor you have in your attic -- 1, 8, 16, 24, and 32 are your options. Try 16 or 24 to start by editing your xorg.conf file in /etc/X11/xorg.conf.
It is always helpful to know what hardware (monitor) you are using, your syncs may be wrong, in spite of what you think.