Krylon plastic paint with Fusion. That's the best paint solution but after time will still scuff, crack and chip. Or you could get a bunch of paint pens and a gallon of coffee. Stickers and vinyl topsheet skins will also work but will peel up if to close to the board's edge after time.
The thing is that snowboards get scratched, dinged and chipped on a regular basis. Lift lines, chair rides and gondola loading are not nice to snowboard topsheets. Whatever you do to make your board look better keep in mind that some asshat will probably ride straight into it your next time on the hill.