I regret it so much my guts turned green. (I deeply regret it.)
Tips
usage
肠子悔青了 (guts turned green from regret) is a very common vivid expression for deep regret. 肠子 also appears in food: 香肠 (sausage), 灌肠 (stuffed intestine).
memory
The flesh radical 月 (meat) + 昜 (yang/bright) - the bright insides of the body.
