Ability to add a caption to thumbnail images

It would be great to be able to add a caption to thumbnail images for a product.  Then, add a site setting to enable or disable displaying the captions...alternatively it could be disabled with CSS as long as the caption was given a consistent class.
 
This would be extremely useful for apparel images, as then I could add the color name that would automatically appear under the image.  As it is, I have to manually add that information within Photoshop before upload.