Is there any app or trick to color Finder tabs?
A Finder tab doesn't display the folder icon, just the folder name. However, you can use a workaround (which may be helpful in a specific and limited use case).
You can add an Emoji character as part of, or at the beginning of the folder name to have it visually distinguished and easily identifiable. Here I have three folders with similar names, that I often keep my files in, and work with simultaneously. I have added different Emoji characters to all three of them to easily distinguish between them at a glance.