Best to coat the base color first, the lightest is a good idea first. Follow with the next darkest and go that way. Allow to fully dry between coats and masks. If you plan it out correctly the original masking will remain on until the very end after the darkest color is on.
Some will spray a flat clear between coats to seal the masking and stop any bleed through.
Because the paint is built up in layers you may want to ‘cut’ the mask lines carefully with a new #11 hobby blade. be super careful lifting the masking, find a corner & lift with a toothpick and NOT something metal! Pull gently close to the surface at a 45 degree angle.
Sanding may be needed after as there will be ridges between colors, use wet paper at around 1200 grit.
I did it the same way SF suggested. I used 4 colors(shades of grey). Hard to see the difference between the two lighter and two darker colors, in the pic. I sprayed the lightest color first, masked off alittle more than 1/4th (not quite 1/3rd) then sprayed another shade of light grey, then masked about 1/4th again, and so on.
I cut a mess of squares and rectangles of all sizes (smallish) and tediously placed them, being very careful to keep everything straight and in line. I sprayed fairly lightly, so not to build up paint along the mask, sanding was minimum.