Colorful bleaching, as it's known, was covered in the documentary Chasing Coral, which showed a whole reef turning fluorescent.

When corals lose their algae due to stress, the excess light travels back and forth inside the coral tissue, reflected by the white skeleton.

If the coral cells can still carry out at least some of their normal functions during bleaching, the increased internal light levels boost the production of colourful pigments which protect the coral from light damage, forming a kind of sunscreen layer that allows algae to return.

As the recovering algae start absorbing light for photosynthesis again, light levels inside the coral drop, and so the coral stops producing as much of these colourful pigments.

But it's not just heat stress that can cause colourful bleaching.

Different members of the coral community can display different colours during these events, while some species don't produce these colourful protective pigments at all.

Even so, these different variants often occur side-by-side, which is why some corals bleach colourful while their neighbours turn white.

The good news is that colourful bleached reefs seem more likely to recover than corals that bleach white, since they tend to appear when heat stress isn't so severe and the colourful pigments themselves offer protection.

Now that we know that nutrient levels can affect colourful bleaching too, we can more easily pinpoint cases where heat stress might have been aggravated by poor water quality.