As this mod delves into legacy block textures that are unavailable through the Programmer Art resource pack, I would like to suggest some of the old coral block textures for legacy blocks:

• The Java Edition 18w09a textures for all five coral variants, and the singular dead variant. These can be seen in this snapshot video by dev SlicedLime or on the Minecraft wiki. They aren't the most realistic representations of coral when compared to the vanilla coral blocks, but they do have unique and interesting textures.
• The Bedrock Edition beta 1.2.14.2 horn coral block, which used a different texture from the Java Edition horn coral block. This can also be seen on the Minecraft wiki. I simply find it interesting.~