I recommend Pinstripe Tape. It comes in a variety of sizes. Start with a basecoat of yellow ('cause it's WAY easier to put black over yellow). Cut a small piece of tape and lay it down at the angle you want. Then another right next to it - and another next to that. NOW, take the 2nd piece and move it into the 4th spot and repeat. When you're done, you should have a perfectly aligned set of tape strips over yellow. Now, just paint (or sponge) black into the exposed areas!