Items you're holding go black when you walk on soul sand

Items your holding go black when you walk on soul sand.

What I expected to happen was that items should stay the same colour.
What happened was that items (and my hand) went black. Also the sky went dark as if I was underwater however not as dark. If you go into F5 mode your hand is seen as normal.

1. Place soul sand on the ground and step on it.
2. Your hand, items in your hand and the sky will go black.