I like the Only Connect walls, but if they're all called variations on 'An Only Connect Wall' then it's difficult to distinguish them from one another.
Thoughts about ways of choosing distinctive titles?
I believe that it would be useful for the title to include two or three words from the puzzle, which might or might not be part of a group. For example, this one might be titled "Black Book", "Red Shift", "Shift Shaft" or "Red Green Alternate".
Perhaps a way to distinguish them would be to add little "story" and use that to title it?
ie: Bob got on this gameshow...now he's confused on how to group them.
or give one of the 4 groups and use it to title the puzzle as a whole?
ie: red, green, blue, yellow are all colors. what are the other 3 groups?
or another possibility with the group option would be to reveal a group, but not which ones are a part of it. (which still simplifies the puzzle, but less so than straight up giving a group and it's members.)
Otherwise that's a pretty tough question since finding the subjects is the goal of the puzzle.