This is a great quick project to to with a pallet.
First, find a pallet that is in good shape. You want to find one that doesn't have nails sticking out and broken or splinter wood.
Next, sand all the rough edges. This takes about 10 or 15 minutes but is but makes it easier to paint and removes some potentially dangerous parts.
Third, start painting. You either brush or spray paint. If you use a brush I recommend painting the 2 x 4 supports so that it blends better. If you are using spray paint you will want to cover the parts you are not painting. You can use cardboard to cover the wood you don't want painted. I would start with your blue rectangle first then paint your strips.
Finally, you can paint the stars on. We just hand did the white as we were going. We like the homemade we did it ourselves look. If you want it to look a little more defined you could create a template out out cardboard and just paint them on. If you are using spray paint you will want you template big enough to cover the spray area. This way you won't have paint around the edge of the template.
Good luck!.