There aren't many different usergroups, though. We'll be building a BS-calling group, yes, and there's the old "cool" group and the new "cool" group in dark green and blue. All other colors are for admins or ex-admins, of which there are few. If you're seeing tons of colors around, then the problem is that nobody except the admins and privileged are talking. ;p
I am willing to agree that the contrast is occasionally high as I look at the Proto Good Future skin, but the idea of alternating row/post colors that are only slightly different is common to many forums and serves as a visual aid, so I won't slander the idea itself.