Dark Mode. Or better yet, multiple themes to choose from. Every Snaplex could have a different color background. Sometimes I switch between Dev, Cert, Prod and have made changes in one thinking I am in another! Having each snaplex being even slightly different in color would help with this.
Do you mean each Snaplex or each org (or both)?
Some customers have different orgs for Dev/Test/Prod and within each org have multiple Snaplexes.
And would you want this as a user setting or a global setting?
At the org level yeah! User level would be a good place to put the options as everyone has their own preference when it comes to colors. I can see managers wanting to impose a standard for teams to be consistent though and maybe use the same theme for each org.