Good question. You can do both, but because it's too cold to spray outside and you get divorced when spraying inside... I brushed. I thought about it... but I brushed.
Michael and Glenn told me about Home Depot Behr paint samplers. They are an enamel-like finish acrylic paint and primer. It says on the label "Interior/Exterior Semi-Gloss Enamel"... but they actually mean "Enamel-like Finish"... they were just too cheap to use a couple of extra words that would clear up a tons of questions. They come in 207ml jars and Home Depot will mix any colour.
I used 2 coats of the base white flat to cover all the blue, silver and black. Then one coat of the yellow and 2 of the red. Yellow covers well enough... probably could have used a second coat but you can't really tell. Red did not cover as well so had to put on 2 coats. I bought a couple of packs of foam brushes from the dollar store. I used green Frog tape for masking and used a small dental tool to press down the edges a bit... and always removed the tape when the paint was wet. It never lifted the yellow or red paint from the white coat. But on the Seabee I just painted, since it was white foam, I did not have to use a base coat... and the tape lifted paint from the foam... so I couldn't mask and just brushed a bit more carefully.
All the paint added about 3oz to the overall weight but you cannot tell in flight.