Male peacock spiders compete to attract mates via elaborate dance displays that show off their stunningly colorful abdomens. Males evolved both brilliant colors and a deep velvety black that provides maximal contrast.
Super black locally eliminates white specular highlights, reference points used to calibrate color perception, making nearby colors appear so bright they’re practically glowing. ~ American evolutionary biologist Dakota McCoy
The ultrablack effect is achieved by nanometric bumps which more thoroughly absorb light than smooth textures. These nanostructures bounce light around and diffract it in a way that evades the view of an onlooker. And the bumps are microlenses which angle entering light so that the light traverses a longer path and spends more time interacting with light-absorbing black melanin pigment than it would on a flat surface.
The luxe look of peacock spiders resembles birds of paradise, which convergently evolved similar nanostructures for their ultrablack feathers. Anti-reflective microlenses independently evolved for flower petals, tropical shade plant leaves, light-sensitive nodules on sea star arms, and ommatidia in moth eyes.