It seems the speech bubbles turn white when she’s being positive or expressing her true feelings instead of being caustic or responding to the reader
CHIRP
CHIRPWhat?, What's with that relieved look on your faceAs long as you're useful to me, you won't have to worry about thatDo try your bestGUUUuuuuuMorningDid you think I would be gone when you woke up ?