Andy Bell set out to convert all the hex colors (like #FFFFFF for white) into p3 colors and wrote up his process:
I’ll be honest. I am not smart enough to explain the new colour systems that CSS has in its ever-expanding toolset. What I can do though, is show you what a major impact they can have with not much effort.
Andy also links to hexp3.com which lets ya pass in any hex value and it’ll do its best to transform it into a p3 color.