I mean just in general. If you look at the avatar I'm using at the moment, you can see the colors that I would prefer to use, but of course that's just my own preference. These colors here at the site cause a ton of cognitive dissonance with me:
I'm always using ChessBase, and this is what their default board looks like:
Not exactly blue, but in that ballpark, and it has a totally different feel.
It's a common feature in most chess GUIs to be able to specify what the dark-square color is, and the light-square color, as well as the border, etc. That's what I'm referring to. I appreciate what you're saying, though. If there were more color schemes it might not be an issue. Possibly the reason that they have such a limited selection is so as not to overwhelm the user. A Custom... setting, however, would give people advanced features without those features extending into the rest of the GUI.
I don't know how hard it would be to set that up, but for instance there are so many different ways to do a blue theme that to have only one available as a plain color is irritating at best.