Inside the house is where acrylic shines. It dries faster than other types, and it keeps its color better, without yellowing. One disadvantage: It costs more.
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.
Cheaper then doing it yourself. Some would argue that if you're going to all the trouble to fully prep the car yourself, then why not just shoot the paint as well? Why get a shop involved? The answer is simply that you'll get a better job and for less money. Some would argue with this, but the fact is that if you've never sprayed a car before then your first car will have a steep, and expensive learning curve. Laying down an even, consistent coat of paint takes considerable practice. Also, paint and equipment is not cheap. You'll need to buy primer, color coat, clear coat, reducers & catalysts. None of these are inexpensive and you can easily spend as much in paint materials alone as the cheapest paint job at Maaco or similar shop.
Cold water paints of the casein type may be applied either directly to a plastered surface, or the surface may be first given a coat of primer-sealer to equalize uneven suction effects. The same is true of resin-emulsion paints, with the recommendations of the manufacturer of the product being given preference in case of doubt. Since resin-emulsion paints usually contain some oil in the binder, they should ordinarily be applied only to plaster which has dried thoroughly.
If paints have been allowed to stand and hard lumps or skin have formed, the skin or scum should be removed, after which the paint can be stirred and strained through screen wire or through one or two thicknesses of cheesecloth.
Color can make a big difference in your life. I know from experience. Before I learned my right colors, I had a closet full of right and wrong colors. Of course, the colors did not work together and definitely did not coordinate. I had no idea of the difference that coordinated colors can make. Further, I had a drawer full of lipsticks some with gold undertones and some with blue undertones.
Paint Selection. Most paints are purchased ready-mixed but, in their selection, consideration should be given to the fact that surfaces vary in their adaptability to paint and atmospheric or other conditions having an adverse effect on paint performance. In addition to the normal weathering action of sun and rain, outside house paints are sometimes exposed to other attacking elements, such as corrosive fumes from factories or excessive amounts of wind-driven dust.