In python the default recursion limit is 1000. This kata has trees with sizes that will make your solution recurse much more than that ;)

Not a kata issue, it's just how python works.
Default arguments are evaluated only ONCE, this means your set is always the same set in every invocation of the function.

Read more here. (notice the Important warning)

Yeah, I spent considerable time searching for how to restrict the values to the valid colors and flavors. Btw can anyone tell me how?

The simple fact that typical insert/update/delete commands aren't enough is an argument yoou need some wider knowledge and looking for it is a waste of time. If You want to copy/paste the solution - ok, it's not college, you don't get certificate for completing katas, however if you're doing exercises (eg. katas) and want to master your skills, you have to have those skills first and get fluent with them by comming up with solutions. So hints would be cool. However - it's Your kata (and it's cool it is here), so You're the boss.

This Kata is clearly not for 7kyu level, period. It contains knowledge beyond 7kyu as diggi55 stated.

done

Approved.

I updated the fork (I hope I didn't miss something more).

Input argument is still different between solution setup, and proposed solution and tets' reference solution. I think they would have to be unified?

It's incredible this has not been pointed out already... It seems all submitted solutions use long[].

Fixed in this new fork: https://www.codewars.com/kumite/62642a1d9eeaacb9fba24199?sel=626661e111cd440023a74f54

I only changed the function type in solution set up, I think it's enough (but I'm bad in C#). Please review and approve.

It would only be reasonable to add a hint about having to solve this with...

It'd not be reasonable at all. My job as the kata's author is to make sure that the kata is solvable, i.e. the tests are working correctly and the description explains the task sufficiently for a competent user (in terms of programming/language/scientific knowledge) to know what to do. Your lack of knowledge or inability to apply it correctly to solve the kata is your own problem which doesn't concern me one bit.

thanks! will do

Thanks, approved !

No, I'm not going to do that. All SQL katas which say "use this particular feature" effectively turn the task into copy-pasting code from the documentation rather than actually learing/researching/coming up with a solution yourself. Such approach to authoring is low-effort and bad, hence I'm not going to do the same thing just to make it "fair for everyone".