Sorry about the late reply. I just don't really have anything to say when it comes to Themes. It's just to hard to manage the ones we have. If I need to make a slight change to one theme, I have to make it on all of them and it's pretty time-consuming. If I was making the site from scratch, I just wouldn't have any.
As pointed out, we can't change the themes on the homepage. You'd need to use the CSS file on the forum and change it to the scheme you want. Even then, you'd have to create something pretty special to make me notice. Look at the Giger theme. That's probably the most unique one we have and pretty complicated too.