What kind and brand of paint is it? If it's quite opaque then you might get away with just repainting it, but you will end up with it being fairly thick, otherwise you might want to strip or sand things back a bit, depending on wether it's enamel, acrylic or Lacquer based. If it's the later two you can strip it easily enough with Isopropyl alcohol using a Qtip, I've done that a lot and it's not that messy if you take your time, or if it's enamel sanding down the grey areas would work well enough.