I just installed Mate on a Raspberry Pi. I installed it on a Debian headless version, not the LXDE version.
My background looks like it's color depth is 8 bit. I look at the same background in Eye of Mate and it looks great, so I don't think it is xorg issue.
Even if I do a vertical gradient from gray to pink I see bands as it changes color rather than a smooth transition.
It also looks like 8 bit on the login screen, but I can live with that.
How can I fix this?