I don't think it's possible to tell from the picture, but if it's a decal, you should be able to tell as it would probably be slightly raised from the surface of the rest of the frame. If you want a decal of similar style, contact a print or advertising company in your area (or find one online), many of them are able to make custom decals. My highschool even had the machinery for cutting custom vinyl decals, so you might want to check with local highschools or college (preferably one with a graphic design programme) to see if you can get one done by a student for cheaper.
If it's painted on, this basic method for accomplishing this is to apply the different colours in layers. Since the frame is black, they would most likely apply the black first. Then they would apply a mask that would block out all the parts they want to remain black, and put on the next color. The same would be done for all subsequent colours. Then they would apply a clear coat on top for protecting the paint.