Dragons come in all colors and different colors may or may not denote different species. Simply tagging with dragon and a color_scales tag (e.g. green_scales) should cover most cases.

However in some universes, such as dungeons_and_dragons, each color of dragon is a different species with unique traits. In those cases, attach a suffix denoting the originating series/universe from which the dragon species originates (e.g. gold_dragon_(d&d))