There's no built-in color picker in perspective, but I made one:
You may want to adjust a few things, like the color names and button text, which are probably in French.
It's been a while so I'm not exactly sure what's included, but I think there's a view that's intended to be used as a popup, with the "valider" button sending a message with the color code in the payload.
Open it and check inside to see what's what, there's nothing complicated about it.