Where's the screenshot?
Anyway, there is no perfect way to change the text colour of the infobar, and the strings themselves are pretty much impossible. This is because the infobar uses HTML to display its text, and WLM doesn't appear to have the HTML bits in its string tables.
The best you can do is replace all colours with the rgb values "51,51,51" or "0,136,228" in the SkinInfo with whatever you want.
A warning though, I've just found out that if your contacts have coloured nicknames the text will turn black (not the grey that WLM usually uses, mentioned above). This appears to be something to do with Plus! itself as it parses the colour tags.