Nick coloring
 

I want to be able to set individual username colour without creating new usergroup.
Is it possible in already existing mods?

search "color" in "all mods" "titles only" and this should help - Users Choose Username Font/Color Posts
Just modify the template edits to be vB4 syntax.

So, I'm looking for equivalent of $post[musername] in vB 4.0.

Yeah.... {vb:raw post.musername}

So, I added new profile field, filled it for one user, found variable, added condition (with vb4 syntax) and nothing changed.
Could someone help me?

You need to be much more specific about what you have done. Images help. And post the exact code you used and let us know exactly what template you put it in and where. There are soooo many reasons this couldn't have worked and so we need details of exactly what you've done.

I edited postbit_legacy template, but I suppose I should modify definition of {vb:raw post.musername}