They may also attract pollinators. Western Hummingbirds are attracted to red. I got buzzed frequently when I lived in Montana because I had a red back-pack. Some Perianth parts have pigmentation patterns which guide pollinators directly to reproductive structures. These are not always apparent with visible light.
Some insects can perceive ultraviolet patterns that are invisible to humans.
It is not readily apparent that the color pattern of Aristolochia flowers provides guidelines for pollinating insects. However, if you trace the lighter areas you can see that they converge on the opening of a tube that leads to the reproductive structures. The Strange Case of Aristolochia Aristolochia sp. This Guides Insects towards the throat. A foul aroma is produced by Osmophores that are near the Androecium and Gynoecium.