on roster window implement eugenia's colors as default and keep these colors for second account
and maybe add another "color-pair" for a third possible accounts, and then just repeat.
most users have one jabber account
if we don't like this, then maybe stick to same colors for every account, add Eugenia's as default, have custom colors (as we do now), and propose some themes [like the one we have now as alternative to Eugenia's proposal]
that's all folks :)