Howdy there Roger 😀
Picture bad glare.
Soo. First a photography tip. Never take a picture facing the sun.
Bamboo, yellow, Right ???
Either cold weather, butt more likely due to being shaded from what you cut off in front of them.
I can't see, how far you pruned them back, butt ! Personally, I would trim them back a couple feet more than wanted, then I wouldn't have so much to cut back every year, or better yet ! Twice a year, or more, since they grow so fast.👍
Good day 😀
😎😎😎