Need help, custom masks

Other than the black border around the logo, it would be pretty easy. Mask and paint the whole thing as a white rectangle rotated 45 degrees, then put a piece of masking tape corner to corner, and spray the blue and red. If it was any color but white I'd say start with a black rectangle and then a smaller white rectangle, but you know how white over black is going to work

For the black border, assuming you want to paint it and not use a stripe decal, I think I'd use three pieces of tape on each side, one of them cut the width of the black border. Lay one down on the inside or outside edge of the border. Lay the thin piece of tape down right against the first one, then lay another piece down right against the thin one. Pull the thin one up and the distance between the two remaining should be straight and even.

If you know the exact size of the rectangle you need I can lay out some templates on the CAD/D system here.

Thanks for the tips Scott. I too was very wary of the black outline, but to be honest, I have to double-check my sources as to whether there actually IS a border or not
As for the dimensions of the rectangle, rotated 45 degrees, from corner to corner, the ideal would be 1cm tall...

Don't know how much help it will be (I didn't expect something only 1cm tall ) but if you save the image below and print it at 1000 dpi it should be exactly 1cm tall. The black image to the right is about 1mm wider to give a black border.