Discussing graphics in a dedicated forum post is definitely the way to go in my opinion, after which a final and concrete conclusions are recorded as GitHub issues and documented in the wiki (this one’s an important point). I think it has been that way for a long time but has since been a neglected practice. Microbe backgrounds for example has multiple related threads spanning years, which I’m also surprised to find out tbh (according to the search bar) with the oldest being 2016! Only problem being not much activity goes on, on those threads.
I do agree that GitHub issues need to be as detailed as possible, it would be ideal to have artists or proponents of such ingame changes to write them in some sort of a “proposal” format.