When the player goes a certain distance away from the main end island, the ender dragon and endermen will be located inside of the fog. Unlike in earlier versions, both will be visible in the fog, colored in purple. Also, the ender dragon is not rendered correctly in the fog: It appears as if its wings were rectangular with purple transparent parts around the normal outline.

Edit: This also happens with both mobs in the nether and overworld fog. I could also reproduce it with spiders.