Perhaps not all of them though. china_dress and dress describe two different kinds of dresses, so maybe they should stay unimplicated. The following tags, however, should obviously implicate dress.

pink_dress
red_dress
blue_dress
green_dress
yellow_dress
purple_dress
brown_dress
multicolored_dress
strapless_dress
open_dress
open-back_dress

I'd say like you're right. gray_dress should probably be included even though it has 1 post only.

Changed it to grey_dress for consistency with the other "grey" tags.

Done.