I have noticed that I have dithering artifacts in q3 arena when playing on my voodoo2 SLI,did some research,and found out those are caused by using a 4x4 dither matrix when performing the 24-bit color to native 16-bit color scaling.I have learned that forcing a 2x2 dither matrix will fix those artifacts.
if someone knows an envvar for forcing the 2x2 dither matrix,let me know..

some screens,q3 arena:

4x4 dither matrix



2x2 dither matrix