On a 220v line, the red and black are both 110 sources. With my wiring, I chose a wire that was just black/white/ground (12/2 or 10/2 I think). I also used a 30A 3 prong plug.
There is no neutral wiring needed in a 220v compressor circuit,(other appliances may require it because part of them do utilize just one of the 110v lines for a typical 110v circuit)
The ground wire is like normal and goes from the ground screw on the compressor to the ground strip in the service panel.
So in your case, red and black would go to the compressor white and black. Ground from plug goes to ground on compressor, and the neutral in the outlet is not needed so no connection is required on the 4th prong on the plug.
If you are still confused, Here are pictures of mine...
Outlet and plug
Compressor connection (and yes, I know I need to change the wire clamp on the compressor, lol)
Outlet wiring (in this case, black and white are interchangeable)
plug wiring (once again, black/white interchangeable, as you can tell the plug/outlet have them switched)
Double breaker (same black and white that run to the outlet. Also notice 30A breaker to match the outlet and that the wires are the thickest in the whole box)
Black sheathed wiring in top right corner is the compressor line (notice only black/white/bare)
Thicker bare wire up top is the compressor ground (5th terminal down)
overall view of the service panel
