I would make them redheads. Are redheads dumb, yeah kinda like teal are, let's say they're forgiving. I have noticed on many hunts that they will land with the redhead decoys if you have them, so you can kind of control the kill zone. I would go redhead because the body shape is much closer to a mallard than a bluebill is.
The whole process. Skip what is too much for you.
- Wire wheel (angle grinder or dremel) or sandblast the plastics to scuff to help hold paint. If neither of those are at your disposal use 150 grit sandpaper. You don't have to spend a lot of time on this step, but you do want "full coverage."
- wearing latex gloves, wash them with liquid dish soap. Do not touch the decoys with your bare hands during or after washing. (keep your skin oil off the plastic)
- get three rattle cans of krylon fusion. grey, black, red (to match the head, not fire engine red, more of a rust color)
- paint the heads red first. so you don't get red on the rest of the bird later.
- paint most of the body grey
- paint the tail section and breast section black
by painting in this order, if you get a little overspray of black on the grey, it'll look like you did a blend on purpose. getting grey overspray on the black won't look as good.
now you are left with the bill and eyes, if you want to go to that much detail. if you don't want to brush the bill, paint it grey before painting the head red. for the bill and eyes use either cheap acrylic paint (it will wear off over time) or get testor's hobby enamel from michaels, hobby lobby, etc. If you don't find a match or don't want to buy an extra color for the blue on the bill, mix black and white, the right ratios of that will give you the blue-grey of the bill.
this is not how you would paint hand carved decoys but it will give you a quick and rewarding diver rig.
be careful, messing with decoys is addictive. this is how i got my start 5 years ago (paint is still shiny wet):