Choosing custom colors

Good afternoon, I want my clients to choose a color for a piece of furniture. For an extra charge, they can request a custom color. How can I have that as an option in my variable product? I could also do this as an Add On.

Whichever way I plan on doing this, I need the costumer to choose this custom color from a list given to me by my paint provider. Basically, they have to choose a color that this company has. Any ideas on how I could do this? Any information would be greatly appreciated!

Esteban