Clean surface of tray with a tack cloth. Use painter's tape to mask stripes across the bottom of the tray and up the sides. Yellow and green tape from FrogTape work well on a variety of surfaces, including metal. Press the tape firmly to the surface to ensure paint doesn't seep underneath. This galvanized tray is slightly rough, but if your metal is shiny and smooth, first sand areas to be painted with fine-grit sandpaper and wipe with a tack cloth.
Using an artist's paintbrush or foam brush, apply a rust-inhibiting primer between the taped lines. Drag the brush parallel to the tape to prevent paint from seeping under. When dry, apply a variety of colors in semigloss latex paint. Remove tape when dry.
To protect the painted lines, spray a clear polyurethane sealer over the surface. Let dry. Because paint is not food-safe, place food on dishware before setting it in the tray.