I don’t know if this is the right category, but I haven’t found anything on this topic. I would be happy if Horizon would offer real colors. Everyone knows the problem of not being able to get a certain yellow or green orange etc. It would even be better to have original colors with the manufacturer’s name. Gran Turismo shows the way 
The same with the rims.
Hey there.
There is this spreadsheet with almost all OEM real life colors, which you can use ingame.
Most of the colors appear in game like they are in reallife. I love this spreadsheet and I am using it all the time to get specific color for my car.