Minecraft wiki entry for Terracotta, associated text: The first picture of terracotta tweeted by Dinnerbone.
The 13w17a banner, featuring terracotta.
The 13w19a banner, featuring stained terracotta. Notice Grumm behind the red wool.
The 13w37a banner showing terracotta in a badlands biome.
Development screenshot of terracotta and other new blocks.