Prismarine and Dark Prismarine have their colours switched on maps

On maps, the colours displayed by Prismarine blocks and Dark Prismarine blocks are switched. This is also the case for their slabs and stairs, and Prismarine Bricks have the expected colour.

What I expected to happen was...:
I thought that Dark Prismarine would appear darker than Prismarine.

What actually happened was...:
The inverse was true.

Steps to Reproduce:
1. Place Prismarine and Dark Prismarine in the world.
2. Make a map in the area with the Prismarine and Dark Prismarine you have placed down, so that both are visible