The colors shouldn't be washed out. I think it's some sort of semi-rare windows configuration error or bug.You didn't get washed out color when you turned on HDR in windows? What TV do you have? C9 or CX?
Back when PG27UQ was new and people were discussing early windows/game HDR, some people complained about washed out colors in hdr, but it never happened to me (nor most people).
About one year later, something bugged out and i had very washed out colors in windows and games, rebooted, gone. happened twice in over two years to me, while others seemed to have it permanently.
I can't recall anyone ever figuring out exactly what the problem was, so the best to do is clean driver install, uninstall any non-essential display/driver related stuff, worst case reinstall/reset windows.