A female Closterocerus coffeellae, a fly, looks drab against a white background and shines against black

Tiny wasps and flies look bland at first glance like any drab brown insect you'd swat away without a second thought. But a closer look reveals a dazzling secret: Colorful wings that have gone unnoticed by scientists for decades.
Researchers at Lund University in Sweden have discovered that the insect species hymenoptera wasps and diptera flies they've been studying for decades reflect light off their wings in rainbow-like patterns. The effect is a bit like oil on water, but these patterns are permanent, suggesting they may play a role in insect communication.

Source: LiveScience