author dependent text styles

this blog has two main authors/editors/contributers.

i’d like to have for each author(user) another display style, so posts are distinctive by color, font and style, without the author having to set that in the editor.

can that be done and if so, how?

the nearest i can get, is the fact that normaly an entry displays with

<div class="entry fix">
   ....
</div>
<!-- /entry -->

my guess would be that it would be possible to set that to something like

<div class="user-5">

is that the right way… is there a plugin that does the trick so i can set it in userpreferences ????