You literally said there's an infinite number of colors. If you're comparing colors to stories, then there's an infinite number of stories. Any number subtracted from infinity still leaves infinity.
But more prosaically, if you can't rely on a tired trope like slavery, then you learn to be creative by bringing in other things. I have players who have a fair number of things they don't want to see in games, based on everything from phobias to trauma. I mostly run horror and sadly, some of those things make for great horror plots. For instance, possession is a no-go at our table due to religion-based trauma. But possession is also an overdone trope, so my horror games become less tired and more original by having to find plots that don't rely on it.
If you can't use red anymore, then maybe that's a good thing, because red is used far too much.