If the spots wash off and reappear the next day, it might possibly be frass (caterpillar poop) from larvae, such as cabbage looper or imported cabbage worm. Check the undersides of leaves for the critters, also for small or ragged holes in the leaves.
This site shows a photo of the frass on a cauliflower head; scroll down to "Damage" and click on the photo at the right (Figure 12). It also tells how to control these pests:
If the spots wash off and reappear the next day, it might possibly be frass (caterpillar poop) from larvae, such as cabbage looper or imported cabbage worm. Check the undersides of leaves for the critters, also for small or ragged holes in the leaves.
This site shows a photo of the frass on a cauliflower head; scroll down to "Damage" and click on the photo at the right (Figure 12). It also tells how to control these pests:
http://www.extension.umn.edu/garden/insects/find/caterpillar-pests-of-cole-crops-in-home-gardens/