A selection of colors wouldn't work for me. When I search for plants with foliage of unusual colors, I want to see all of them at once. I don't want to have to look for each specific color, especially in view of the way some people misuse the "Other" boxes on the data form. They might ignore "Russet" and type in "Other: Mahogany" or choose to enter "Other: Slate Gray" instead of simply checking the "Gray" box. I couldn't begin to guess all of the fanciful color names they might come up with, and my search would therefore be incomplete.
I already run into that problem when I search for a particular flower color. When I search for blue blooms, for instance, there are some plants that are conspicuously absent from the results. I know they're blue, however, so I look for them. When I go to the entry, I find that someone entered "Other: Cobalt Blue" or "Other: Powder Blue" instead of checking the "Blue" box.