You can type either hex or RGB values into either of the text fields and the colours will be updated accordingly. This works like a Hex converter, so you can insert either type of value in the appropriate field. Once on the clipboard you can paste the figures in the appropriate place as Parameters for other applets. As you can see the are Three types of background colours , light and dark, choose whichever is appropriate to you. These represent the highlight or lowlight versions of the colours.
Different components use either one or the other.