I think using a blue logo looks like crap in an all blue forum. It's like dropping lakewater into the ocean and expecting to tell the difference. Maybe? Or that's just a crappy analogy.
I don't consider myself a designer, so take with much salt, but the basic principle of logos I was taught is that the colours of the logo should dictate the colours of the site. So from that point of view, a blue site should have a blue Duke. But I'm so used to Duke's nose being red that the blue one just makes me think he's freezing cold, which I why I've gone for a red one.
How about putting one of the three (at random) at the head of the forums temporarily to give us a better idea of what we're voting for?
Can anyone produce a user stylesheet which does the effect? I tried with the Stylish plugin for Firefox, but I can't get it working. I can hide the existing image, but my attempts to use :after aren't producing any visual effect whatsoever.