Touching up paint isn't too difficult but it can be tricky finding a paint that matches your color. This is because not all bicycle manufacturers provide touch-up paint. We'll try to find it for you, but if we can't, we suggest visiting an auto-parts store and checking their selection of automobile touch-up paint. Often, you'll find a good match there. Another touch-up alternative is nail polish, which comes in many hues and is easily applied.
When you've found a color match, check the chipped spot for corrosion. Any rust will need to be gently sanded off (don't scuff up the surrounding area). Then, carefully apply the paint by putting on a thin layer, letting it dry and repeating until you've filled the chip.
Don't expect the chip to disappear. You'll still be able to see the edges. But, from a few feet away, the paintjob should look fine. And, the important thing is that you've made your paintjob intact again, which prevents further paint wear and any possible corrosion from developing (not much of a concern on aluminum, carbon and titanium frames).