The color chart and color picker circle are managed by a single sprite. Copy the color picker to your backpack and use in any of your own projects. The color swatch next to the picker shows how to get and use the selected color. Test the color by click and draw in the test area.
Original idea for the color picker came from the Lathe modeler by AddZero. Scratch can't make black and white by setting the color number so I use a flag and set these explicitly.