World changes to pink and black, except mobs, and everything behind barrier blocks turns grayscale.

Occasionally when I leave Minecraft open for about 10 minutes with the screen off (so app is open in background) and then switch back onto it after coming off to put music on from Spotify everything in my world turns black or pink, except mobs, and the blocks in my ineventory lose their textures but instead of displaying the Missing Texture (black and pink checks) texture, they turn pink. The block in my inventory in the screenshots is Stone Bricks. This is a Creative world. All the sounds work right though, and although I wasn't able to get in the screenshots the lava moat in the enrance to my unfinished mansion is pink with parts that flicker from white to turquoise. I fixed this by restarting the world (save and quit and going back to the world from menu). The world preview was in black and pink too. This is fixable but annoying when it happens.