I had some fireworks being duplicated with a command block and was dispensing them into the sky on a flat world. I switched apps to a browser, came back and this happened...

It seems to affect how shadows and light coloring are generated, but I don't know much more. The first image shows the block lighting and coloring messed up, and the second one shows its effect on entity shadows (but not the player's).

This was also captured a bit after the glitch first occurred. For a few minutes, the game couldn't decide on any lighting and would flash lots of different colors and a few light levels.