Out of the box you can control Discourse’s base color scheme as well as the colors available for categories (the
category colors setting). But if you want to use our avatar generation system you either have to live with the somewhat random color assignments, fork the letter-avatar microservice, or create your own randomly-assigned defaults.
It would be nice if there were a site setting that accepts a list of colors (similar to the
category colors setting) that are randomly paired with letters from the avatar generator.