Cordyline with fancy foliage will turn green if given too much high nitrogen plant food or if given too much shade. They also like plenty of water in summer. You can try giving your Ti plants or Cordyline more sun and do not fertilize for the rest of the year. You may see another change in leaf color when colder weather returns. Mine went from raspberry red to green and white in the fall but turned pink again once summer returned. Don't be shy about cutting off the oldest leaves especially if you see new growth coming from the center of the plant that has reverted back to the original pink color. Gardening is full of surprises. Keep growing, Marianne Binetti