You can also use m64config to alter the settings. I just realized that I've been running on 8 bit color for, well, a very long time. I can actually *read text* on Netscape 4.x now!
Of slightly more interest to you might be a recent thread on comp.unix.solaris that indicatest that Evolution will not run on Solaris unless your color depth is set to 24. Something to keep in mind.