These apples are bright with a glow of magical energy. 
Different colored apples have different affects:

Red: Consuming 1 whole will have the same effects of taking a long rest and you regain all your lost health. Consuming half or a crushed version will restore half health and you regain none of your spell slots, and cooking it will render the apple useless; but will taste delicious. 

Green: Consuming 1whole will restore all spell slots. Consuming half or a crushed version will restore all spell slots of 3rd level and lower, and cooking it will render the apple useless; but will taste delicious.

Yellow: Consuming 1 whole will give you 50ft of extra movement for 1H. Consuming a half or a crushed version will grant 25ft of extra movement for 30 minutes, and cooking it will render the apple useless; but will taste delicious.