They don't want you creating images that mimic either works of other artists to an extent that's likely to confuse viewers (or courts), or that mimic realistic photographs to an extent that allows people to generate low-effort fake news. So they impose an intentionally-crappy orange-cyan palette on everything the model generates.

Peak quality in terms of realistic color rendering was probably the initial release of DALL-E 3. Once they saw what was going to happen, they fixed that bug fast.