It depends on what kind of finish it is. If it's nitro, it's easier, because the solvents in nail polish will help hide the fix by 'melting' the edges of the gash. Poly would be a lot harder to fix (but if this were a poly finish, you probably wouldn't have got that chip from a simple knock like that). Also, you can certainly find a marker in the exact shade of your guitar -- there are kits of artist markers with a range of blacks and greys. Just coloring in the gash alone will be enough to hide it. After that, you can fill the dip with anything that will harden -- superglue, nail polish. Do that in several layers, giving each layer the time to dry. You could probably get the repair to where it's almost invisible. Like I said, mask off the rest of the finish so you don't accidently spill any of the superglue/nail polish on it. I don't think you need to color the superglue -- varnishes aren't colored, after all. They're a transparent layer applied on top of the paint. On the other hand, if it IS a nitro finish, then you might as well prepare yourself for other dings/crazing in the future. It's part of what makes nitro such an excellent finish. You can really see the life of your guitar in it. If anyone asks about the ding, just tell 'em you got it diving off the stage in the middle of a wild solo. Or that one of your groupies knocked the guitar over while you were ... um... yeah.