So you’ve built a car. You swapped in just the right engine, got all the trick suspension parts, sat it on some spectacular wheels, and now it’s all back together. But the paint is in a state and now you need to decide what color to paint it.

This is a surprisingly big decision because even by conservative estimates, a new paint job will cost a few grand. So getting the paint scheme just right is important. Fortunately, there are tools you can use to help you make the right decision.

Even if you decide to paint the whole car one color, it will still have to play against your wheels and it can be important for smaller stuff like hoses and accents. But even more importantly, if you decide to go for a two-tone paint job  like VW did on its Type 20 , knowing a little bit of color theory could help you avoid accidentally designing a vehicle that only works in the lead-up to Halloween.
Color theory isn’t exactly a science, but it’s widely used by artists to find colors that work well together and to design colorscapes that are pleasing to the eye and much of it comes back to the color wheel.

Based on red, yellow, and blue, the first color wheel was designed by Isaac Newton in 1666. Starting with those colors, most wheels then expand to include secondary and tertiary colors. Effectively, these are just more complex combinations of red, yellow, and blue.
What’s important about the wheel for you is that over the years artists have found ways of combining colors based on the wheel that are widely seen as pleasing to the eye.

Some of these formulae include keeping to colors that are adjacent on the wheel. Any three colors that touch on the wheel—like, say, blue, indigo, and purple—are called analogous colors. Lotus's early yellow and green racing livery took advantage of this.

Grenadille [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)]​
Complementary colors, meanwhile, sit at opposite ends of the color wheel. Placed side by side on your car, these colors contrast against each other in a way that tends to be seen as pleasing. Think of how the orange pops off the blue of the Gulf Racing livery.

You can also combine these formulae like Martini does with its racing livery. The blue and the lighter blue stripes could be called analogous, while the middle stripe is a complentary red. 

Naturally, this isn’t a hard and fast rule. You can also pick color combinations that happen in nature or, if you’re German, on candy bar wrappers. But it’s worth remembering that the way colors interact will impact how your car, as a whole, looks. Colors may work against each other to wash each other out and make your car look worse than you expected.

It’s also worth remembering that it’s your car, so you’re well within your rights to paint as garishly as you damn well want. Using a color wheel, though, may help you if you’re having any trouble picking the right hue to make your car pop.