If when a player's mining colony plays out, the name of that colony on the mining tab of the economics screen could be highlighted in red, that would pop right out at the player and make identifying empty mining colonies much easier.
It is also a thing, that both CMC and "governmental" mining colony could (and nearly every one would) run into inefficient mode, where remaining accessibility is too low to continue mining really.
For "governmental" colonies we have an option to remove it, but it's not an available option for CMC.
So, I think it will be very cool to have 2 new simple mechanics:
1) Yellow and/or orange color indicators for any mining colony (both commercial and governmental) running at low and/or very low accessibility levels.
and
2) An obligatory or optional (by button) closing of CMC and moving it's complexes to another, more abundant sites.