Order some black flocking, you will not need much, 4oz is more than plenty. Get some rustoleum oil based paint, the small can, I think it's a pint, at the LowesDepot™. Color Gloss Hunter Green. Don't worry about the gloss, it won't turn out gloss with the flocking. If you have to buy the quart it still only around $9.
Get you a 1" chip brush (the crappy disposable 69 cent brush or whatever it costs.)
Quickly paint the green paint on your heads, right over the existing flocking. Don't paint anywhere you don't want flocking (the eyes, bill). Work neatly, but work fast, you don't want the paint to start to skin over.
Over a large tupperware, dump the flocking over the head. Rotate it around in your hand and make sure you really get it on there. Hang/set aside to dry. 99% of what you pour over the head will end up in the tupperware for re-use on your next head. Now move on to the next head, do them one at a time, or the paint will skin and the flocking won't stick.
If your flocking has clumps, use a flour sifter or a piece of porch screen to sift the flocking on the head.
The black flock with the green paint will turn out about what you want. The flocking will be very durable. You might need 2 coats. Rustoleum brushable oil based "stops rust" enamel is about the best flocking glue there is out there.
Flocking decoys is really easy. It's just paint and dump the stuff on them. Boom. You have great looking, durable heads.