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.
Side note, The resource pack I'm using is a self-made one that only changes a few textures. It should not interfere with the breaking animation or biome colours in any way.