The colour schemes aren't really that big of a deal. It could always be a successor Dark Angels chapter or painted green for some specific campaign or something.
Sure there are recommended paint jobs and most people would want their Ravenwing black and their Deathwing off-white but I don't know that almost anyone would complain if you didn't.
I think that is the point of their being the division into chapters. Initially there were the 18 remaining Legions with their colour schemes but once they got broken up there were thousands of chapters so you can pretty much paint them however you want and be within cannon.
With Chaos it is a little different. If you want an VIII Legion force there aren't a ton of options for colour scheme but presumably one of the big reasons for choosing the Night Lords is the colour scheme.
Word Bearers can vary significantly in colour scheme, even having some of your models in the original grey would work.
Same with World Eaters, if you have white and blue world eaters in 40K probably no one would be mad about it.
But even there if you wanted to use the rules for a specific legion but didn't like the colour scheme, like the VIII, you could just use their rules and make them a renegade chapter with the same fighting style.
It's a (deliberately) big universe, however you paint it, you won't be wrong.