Visual Glitch With Blocks

I was trying to build a 3x3 piston door when i saw that it was raining. I the middle of building it i placed a block and it came up black. but when it was almost done raining it turned gray, i found that this only happens at Y=16. This also happens during thunderstorms. Placing a block above this will make it no longer turn gray or black. It will fade back to its original texture.