The Copper Cape is a cape that was given out to promote The Copper Age.
The cape's design depicts a variation of the pattern that appears on chiseled copper and the top of copper chests. This pattern has various stages of oxidization, with the top of the cape depicting copper that is not oxidized, and the bottom of the cape depicting fully oxidized copper. The elytra design uses a similar oxidization gradient, but depicts copper grates instead.
The cape is available both on Bedrock and Java.
(Credit: Minecraft Wiki)