One precaution: You can't paint with it in cold weather. The chemical reaction that transforms the water solution into a durable finish will not take place if the temperature is below 50°. (Conventional oil paints don't stick well in cold weather, either.)
Basically what you're looking for is a good, solid foundation of existing paint that is stable and still strongly bonded to the car. Many times an original factory paint job, even after decades will meet these criteria.
And, its never been more important to know your colors. Why? Because color is back in a big way! Just look at the vast variety of colors in the department stores.
Jaipur School: Gods and goddesses, kings and durbars are very attractively painted on hand made papers by the artists.
Practically every manufacturer has a "color system," a fat book of color chips with instructions for duplicating each chip. This is accomplished by intermixing cans of colored paint, by adding a concentrated color to a can of white or colored paint, or by adding concentrated color or colors to a can of neutral "base" paint. And for those who don't want any guesswork there's the Color Carousel that mixes the paints right in the store. Whatever the method, the result is a range of colors such as no amateur painter has seen.
A flat, semi-gloss, or high-gloss finish may be applied to the primed surface. For a flat finish, two coats of flat wall paint should follow the priming coat. For a semi-gloss finish, one coat of flat wall paint and one coat of semi-gloss paint should be applied to the primed surface. For a high-gloss finish, one coat of semi-gloss paint and one coat of high-gloss enamel should be used over the priming coat.
Your average paint company knows that their most important advertising is done inside the paint retail location. A brand's paint color display (or color wheel) is its best tool to attract you to their paint. How can a paint company use its own color wheel to lure you to their brand? The answer is easy... color. For centuries, advertisers have used bright, bold colors to focus the attention of customers on their brand. The power of bright colors is evident in signs, logos, and almost every form of commercial marketing. This fact is common knowledge, and yet it still comes as a surprise to many people that paint companies use these same tactics to draw your attention to their line of paint colors inside every home improvement store.