Even that doesn't make a ton of sense.One of the benefits of a stolen enemy ship is that you can use it for covert missions by pretending to be the enemy.In fact, that's exactly how they use the thing in the series, which shouldn't work at all given the paint job, but does anyway thanks to the comedic stupidity of stormtroopers.Then please paint them in all colors you like and make them perma-rebel ones.
Obfuscation is for the weak and cowardly.
They are rebels for Wookies' sake; they need to REBEL with colorful panasche!
Except anyone with common sense would report a stolen TIE Fighter, and every com tech and pilot should know how to check their IFF to see that it's not a Imperial TIE without having to see that stupid paint job.