Yellowing topped plants

I topped 6 of my plants last week using a full-top procedure where I cut just above the second node. I'm about 3-4 weeks into the veg, and 6 nodes had developed. The procedure went great and they've been strong and recovering for a week. About three of the plants, however, have begun to yellow and change color. My best guess so far is that they're getting too much light after an intense operation. It can't be nutrient-burn because all other plants are getting the exact same dosage, and they're doing fine. Any ideas?