Recent chat, which has only just started, with Hook on Team-Games has had me thinking on it. Because as a skinner I know a lot of skins that were initially released by fans of the game didn't necessarily have all 4 team colors or any. I like to have all 4 of them, which is why I started learning how to fix that... but when I started posting some of my skins to the House·of·Fools it was pointed out that skins where team colors are less than obvious, aren't as good
So, a few things.
1. It's important that everyone on a team can tell who's with them and who isn't:

2. Some skins' team of choice is a little more subtle than some others, which can be a problem online:

3. If which team you're on is only obvious by whose flag you've got, maybe it can be a problem:

4. It's because of this I'm planning to update one of my 1st skin edits.
The Dark Hero skin was initially made from Chris Ollis' 1st released superhero skin pack (which had no team colors).
I used each hero as a different team color:

For RED I went with Captain America, as he's got a little more red than Superman (BLUE). In-game this can be hard for people new to it:

Fortunately, I eventually found his 2nd superhero (also no team colors) skin pack which has The Flash in it.
Planning to eventually incorporate that into it: