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Why might a grasshopper or moth reveal bright hind wings while escaping?

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A fluffy gray cat clings to the trunk of a tree, looking upward as it climbs to escape. — Avoidance behaviour Cat fleeing by upward climbing.

Grasshoppers and moths often reveal bright hind wings during escape as a form of startle display. When these insects are at rest, their forewings or upper wing surfaces are cryptically colored, allowing them to blend into their surroundings.123

When a predator disturbs the insect, it suddenly exposes the bright, contrasting colors on its hind wings. This rapid transition from a camouflaged appearance to a striking display is intended to startle the attacker, creating a momentary delay that provides the insect with an opportunity to escape. Once the insect lands and hides the bright patches, it effectively "disappears" back into the background, often leaving the predator confused and unable to relocate its prey.24

This behavior, sometimes referred to as flash color, serves as a defensive mechanism to distract pursuers. While some insects use these colors as a warning of toxicity, the primary function during flight is to disrupt the predator's focus and facilitate survival.423