We should add a few new aliases for our colors, e.g., `--purple-60` and `--purple-30`, to remove more media queries. They're needed for example in the pereferences (see https://gitlab.torproject.org/tpo/applications/tor-browser/-/merge_requests/660#note_2909188). We already do it for `--tor-branding-color`, but it's tied to the release channel.