I'll make another version with some massassi colors, but that's way at the end of priorities.
As Deadman said, VB is phasing out support for VB3 entirely, so it was either upgrade or work with a buggy and possibly insecure forum. I am not shooting for a middle ground, I simply opted to bring the forum up to date FIRST, and work on themes second. I gave Massassi something they could use, and will move on from there. Even the theme as is took a significant amount of work, sadly.
Like I said in my first post, the classic green will also come. I just need to finish one theme first. I think the Olive theme is a more pleasant theme overall, so it was made default, but it will by no means be the only choice when I'm finished. I had to start with one, and Olive was it. Once I have finished Olive, I will be able to use it as a base to make the standard Massassi theme, which will significantly reduce the amount of time it takes.
There are several css files. There are also several header templates, and templates inside those templates. Not to mention stylevars are the preferred way of adding and changing CSS now. When they work properly, they are good, but they can be incredibly aggravating to find anything. In short, VB3 was actually easier to modify than VB4, but VB4 will put up with updates better than VB3 did (VB3 required template fixes regularly).