Any way to apply a label without applying a color?

In a recent thread (Any way to search by label without entering search terms?) Christian wrote:

This will be wonderful and very useful, thanks Chrisitan! But with labels becoming “first class citizens” – I’d also welcome the ability to apply labels without adding or changing the color of the thumbnails. Applying color labels to identify and distinguish text icons is understandable – applying color labels to thumbnails of images seems somewhat counterproductive.