This is part of the #1905 meta...
Describe your issue or idea
This idea has been mentioned in the past by @wesruv while building Basis, and also in an unrelated context in https://github.com/backdrop/backdrop-issues/issues/1224#issuecomment-141...
There are php libraries that could help with this:
Expected behavior (if reporting a bug)
When users visit the settings page of a theme that has color.module support, they are presented with a button to upload their favourite image or their company logo. Once uploaded, we extract a color scheme and apply it to the theme. The user can now preview and tweak.