That’s not really true. The regional carriers like Republic and so on have had a variety of different paint jobs (United Express, American Eagle) and it hasn’t

That’s not really true. The regional carriers like Republic and so on have had a variety of different paint jobs (United Express, American Eagle) and it hasn’t been considered an issue. Not to mention the issue of random call signs like Brickyard and so on. And regardless of that we’re talking about codeshares anyways.