I have been trying to change image colors but I noticed something else weird I think – when I inspect the images with firebug I get a whole URL string like this for menu.png
black url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAhCAIAAACX21boAAAAQElEQVQI1z2NwRGAQBDCmLShFmwrlnDFER/u+QMCQ9Zzc5wXSYhiREcbTMeXGtRhxX68ip1s7/7+zvZOYuZH1BdAxkounhk4BgAAAABJRU5ErkJggg==);
that just looks f-ed up. I’ve looked on a few other sites that are using your theme and they have it too
What is it?
From the looks of it that’s just an embedded image so it’s harmless.
The original theme does not contain such code though, the theme was probably downloaded from somewhere else.