Final answer:
The animals that display the most rapid color change are cephalopods, specifically squids and octopuses, capable of altering coloration in under a second for purposes like camouflage and social signaling, largely due to their specialized cells called chromatophores.
Step-by-step explanation:
Animals that display the most rapid color change in the animal kingdom are certain cephalopods, specifically squids and octopuses. These sea creatures can alter their appearance in less than a second with dazzling effects, often for camouflage or social signaling. The change is facilitated by special pigment cells called chromatophores, which can expand or contract rapidly to produce different colors. While chromatophores create pigmentation like yellow, red, brown, and black, the layers underneath, consisting of iridophores and leucophores, reflect light to produce colors such as blue, green, and white. This ability is different from that of chameleons, which also change color but generally not as quickly or as dramatically as cephalopods.