Is there a way to drag to select multiple colors?

[radzo73]

Basically, what I'm looking for is a way to use "Select By Color", but I can drag around to select multiple colors. I'm working with a limited palette (with more than 255 colors, so an Indexed Colormap wouldn't help), but I want to find duplicate colors (i.e two colors that are near-identical and should be one color to make the palette simpler), so using a higher Tolerance defeats the purpose I want.