The bug

When breaking a block of grass, the animation itself seems to take on the colour of the biome colour. In some biomes the effect is stronger than others. The biomes with strongest effect I tested are Forest, Dark forest and Birch forest.

How to reproduce

In a normal creative world, locate a Forest, Dark forest or Birch forest biome for best results. Either find grass blocks, or put multiple down in creative. Then switch to Survival and start the breaking animation. The grass block's breaking animation should be miss-coloured.