My cactus is turning a reddish color.
What Would Cause a Rattail Cactus to Turn Red?
Certified GKH Gardening Expert
Your cactus could be turning a reddish color because it is getting exposed to too much direct sun. If this is the case, I wold move it to a location where it gets filtered sunlight. Your cactus may also be changing color because it is dehydrated and not getting enough water.