Help with color picker in Numbers

[pedzsan]

The attached image shows the color picker that I see in Numbers. Note the bottom two rows of colors. The right 5 on the bottom row are "Unused" or clear. How do I clear the ones that are filled? I can't even figure out how to reuse the ones that are already set. I've tried selecting one and hit delete along with all of the chord keys but it has no effect.

 

[hg.wells]

I don’t think you can clear them, can you not just select the square you want to change the color for and pick a new color?

 

[galad]

The backspace key can delete them.