Measure and mark with a light pencil squares that are the height and width of the tray; for example, each pallet board in project shown is 2” tall and so also measure 2” wide.
Tape off random squares so that you're never taping over wet paint. Tape off some of the squares diagonally.
Using very little paint on your brush, paint each diagonal section of the squares with a different paint color listed.
Tip: There is no rhyme or reason to color selection; when you’re done and all tape is removed it just works out! Don’t overthink the colors!