Simultaneous colours on the colour wheel
For finding the three colours that look best together, you may consult the colour wheel. The three consecutive colours next to each other on the colour wheel or in the colour sequence of the wheel go together well. This usually happens because they are from the same colour family.
Opposite colours on the colour wheel and a third neutral colour
You can also consult the colour wheel to choose two colours opposite each other and then the third colour with a neutral tone. This neutral colour might also be the one that is analogous to the other two. These colours usually go well together because neutral colours anchor the colour combination in the inherently contrasting colours opposite each other in the colour wheel.
You can consult nature and identify colours that emerge within a scene that you find calming. Our bodies respond positively to nature, so colour combinations from nature tend to look best to us.
Colours of similar tone and intensity
When combining colours, consider tone and intensity. Match colours of similar tone and intensity for the most cohesive effect. For example, match deep jewel tones with other jewel tones (e.g. gold with emerald green and indigo) or pastels with pastels. Also, consider “warm” and “cool” tonalities when choosing your colours. Remember, when breaking colour rules or crossing tonal and intensity boundaries, allow two tones to support each other and hold the third for contrast. (See, Is White or Black really a Colour?)
Atypical colours might also look good together
Colours don’t have to “match”; they have to “go”. This means that even colour combinations that seem atypical can look best together. To achieve this successfully, train your aesthetic eye by studying unusual colour combinations in nature and also colour combinations that have been used by fashion, architectural and graphic designers.