If you can see the green caterpillar then most likely it's the cabbage looper. Sometimes called an inchworm. I just flick them off into a coffee can with some detergent and water. You can use BT which kills them by being systemic. That means it is actually inside the plant and the plant is now deadly to the worm. I've never used it since it MUST have some effect on the rest of the world. I'm probably being a bit paranoid there. Try the detergent first. The damage to your plant, going by the picture, isn't severe as yet. By the way, those cute little white butterflies we see all summer are the culprit. Some people spray a little cheap vanilla extract on the plants and it seems to confuse the butterfly (moth). They go everywhere and apparently recognize your brassicas by aroma. Makes sense. Then they lay their eggs and along comes the hungry caterpillar. Hope all this helps somewhat. Best wishes with your plants.

1. You let let it get way too old. 2. While in your climate you may be able to get with away with self wrapping types, heads exposed to sunlight will turn pink to purple when exposed to sun. Cauliflower has a short harvest window. The heads should be good if promptly harvested. If they turn overly quick perhaps you should tie up the heads to keep the sun from reaching them.

Thanks for pointing me in the right direction. Is this buttoning? Probably due to the heat and/or lack of water while sprinklers were being repaired. Are these edible? I am not sure I am brave enough to try!

Some call it "ricing" (fuzzy with leaves in the middle of the head), some call it "buttoning" (button size curds) and some call it bolting if it first looked normal but small. Bottom line it is a response to poor environmental conditions ie: early heat or frost exposure (I'd guess heat in your zone), excess nitrogen, inconsistent soil moisture levels, rootbound when transplanted, etc. Cauliflower can be very picky about its growing conditions. Dave