This bug does not happen in 1.21.2.
Steps to reproduce:
1.Create an custom character (I created an steve);
2.Go to main screen and Close the game;
3.Re-open the game and all of them are going to be red-haired.
I got this bug about 2 times with the method above but it seems that the trigger is so specific that there's another thing that you need to do before closing the game. 
If anyone is having this bug, it would be nice if you can give an comment with more information.

The Steve that's not red-haired is the one I created recently.