In the Colors dialogbox, click the Custom tab, then click in the Colors display to choose a basic color, and use the shading slider to the right to pick the exact shade you want.
Before you are able to launch one of these apps, a standard dialogbox will appear at the top of your screen (just like with geo-location apps) asking for specific (one-time) permission for this (and only this) site to access your camera that you can either allow or deny.