Lane: they're color coded for different size hoses. I can't remember the size-per-color, (Hell, I can't remember resistor color codes anymore, either!) but I know I have several different tiny bins in the shop with all of each color for standard sizes like 1/8" - 3/4" hose, usually in 1/8" increments. Don't know if they came from Harbor Freight or elsewhere like Mechanic's Bliss, but they're out there.
Since the quality standard for pretty much anything coming from China is questionable (for both clamps and hoses), you really have to try the clamp on the hose and see how tight it feels and go from there. They apply pressure pretty equally, so they don't have to be as tight as a Bull's butt in a cloud of flies. I have very seldom had one leak, usually because the hose or metal tube was cruddy.
And as Danny said, they don't destroy the hose like the spiral winder clamps do (especially f you're like me and over-tighten the heck out of them in the first place).
I'm not a big fan of spiral wind clamps, either. Best use I've found for them is to hold my heater ducts together (with no pressure) or as a balancing weight on driveshafts..... 