This isn't a really must-fix bug, but sand turns black during a high fall

Sand is one of the few things that use gravity. I don't know why, it turns black during a fall.
I don't really think it should, but I don't think this glitch is popular, so I posted it because nobody supposedly posted it.

It shouldn't have turned black, but here's how I found it:
I was in a 'Desert Hills Biome', and I saw these layers of stone underneath sand without digging the hill. I broke a column of stone and watched the sand fall. I noticed that the sand casted a shadow in between them, and turned black.