Whoever told you WD-40 needs to be drowned in a bucket of bleach.
What you'e seeing is pretty normal for cheap, un-coated rotors.
Pull off your wheels, and remove the rear rotors. Take some steel wool or sandpaper and clean up the rust. Wipe it down with soap and water, dry it quick. Now, see the shiny part? That's called the SWEPT AREA. That's where the pads grab the rotor to stop your car. Don't touch that area.
In fact, mask that area off with tape - front and rear of rotor. Now, get some GOOD spray paint (rustoleum is good) and paint the rotor (black is a good choice). Give it 2-3 thin coats, let it dry in the sun in between coats.
Unmask the swept area of the rotor. Your rotor should now look like this:
Reinstall. You can do the same to the fronts.
When you eventually buy new rotors, buy a zinc-coated rotor... they'll stay new-looking.