A little bit of History
Don't worry! This is going to be short, although the colour has been studied from the 15th century: how to obtain colours, involving physics, chemistry and even maths. But it's not until the year 1920, that the Bauhaus School developed different theories, about the transmission of the colours and how do we view them, especially the studies of Johannes Itten, a Swiss expressionist.
It's thanks to these studies that we could develop the modern colour theory.
Johannes Itten → Zweiklang 1964
Have you ever done an image in photoshop, but when you print it the colours look different? That's because we have different methods to produce colours, where the primary colours change.
These colours are used by screens, and anything that emits light. The wavelengs of the light create the different tones, and when more light is added, the tone is brighter.
In this palette we consider the primary colours the red, green and blue (RGB). Here, white is the combination of all, and black the absence of colours.
Used by anything that reflects light, like books or other print materials, unlike the additive system here, the pigment determines its colour to the human eye depending on the light reflected.
The primary colours here are: Cyan, Magenta and Yellow (CMY), white is the absence of colour while black is the combination of all colours.
It's important to remember that pigments we have at the moment don't absorb the light completely, because of that when we mix all the colours the closest to black will be a dark, dark brown. To fix that we add a four pigment, which we call Key, hence CMYK, this four pigment is essentially Black.
Primary, Secondary and a lot more
Once we have explained the different systems, it's time to start explaining the different things that compose a colour. Mixing all of this together is when we obtain any possible colour.
This marks the position on the colour wheel, usually on programs, like photoshop, is referred in degrees (because it's a wheel), for example perfect violet is on 270 degrees.
How bright a colour is, usually it goes from 0 to 100%, being 0% the black and the 100% the white.
This components tells us how rich a colour is. Less saturation means the colour becomes a shade of grey, and a perfect colour with the full saturation, the pinkest pink, if you will.
The colour as a chameleon
As you can see on the image; you may think that inside each square, there is a square of different colours but is there?
An important rule when you are painting, the colour changes depending on it's surroundings, this is a well-known optical illusion, the truth is that the colour in the small squares it's the same.
If you think carefully is not necessary to have a deep knowledge about the theory of colour to get beautiful compositions, but it is recommendable, especially on cases like the optical illusion, because one colour can ruin a whole composition. Now I'm going to give a few examples of how to combine the colours, the usual ones. All the Palettes created here are from Adobe Color.
A single hue extended, changing the brightness and saturation.
Colors that are directly oposed in the colour wheel, this example is a simple one but you can create a palette with a double complementary, that consist on the combination of two complementary colour pairs.
Three colours that are equidistant on the colour wheel.
A group of colours that is adyacent to each other.
This is just a small introduction about the theory of colours to create a pallete. You can use the method you like the most or create one in a intuitive way. In my case the ones Ilike the most are the ones created with complementary colours combined with the analogous palette.
I think it's ideal to accentuate a part and create a point of attention. If you want to further investigate how the colour can change depending on its surroundings, you can do the same as in the gif I made.
You can do it with photshop or mixing cartulines of different colours and it's a good exercise when you are starting painting or designing.