I looked it up and you're right. It's called "flash colouration".

Flash colouration. “Flash Pattern”, more commonly called “Flash Colouratioin”, is usually applied to patterns that disrupt an image or startle a predator.
An example of a visual disruption (I can’t think of a better term) is when a moth with cryptically forewings flies off in an instant (no warming-up) and flashes brightly coloured hind wings. Thus is commonlky seen in the underwings (Catocala spp.) . Touch one of these at rest and you see a blur and a flash of bright colour as the moth flies off. Some large yellow-winged grasshoppers use a similar behaviour, very conspicuous when they fly and instantly disappearing when they land.
An example of startling is seen in moths that have eye spots on the hind wings, e.g., some silk moths and some hawk moths. These moths have to warm-up before flight. So, when disturbed they raise the fore wings suddenly to expose the eyes on the hind wings. This supposedly scares predators, especially birds. Owl butterflies have huge eyes that are exposed during their slow flapping flight. Birds typically attacking from behind are confronted by 2 large “owl eyes” as they get close.
The pink spots on the abdomen of the Pink-spotted Hawk Moth is probably an example of warning colouration. When discovered by a predator, the moth exposes its abdomen. Such bright colours advertise that the moth is distatesful. These aposematic colours are common in moths.

For that info.