Colour in design
There are various aspects of colour theory, like primary, secondary and tertiary colours, the difference between tone, hue and value, additive and subtractive colour models and other technical issues. These are all very important rules, and it’s useful to know them. But strictly following the rules of colour harmonies won’t exactly lead you to a perfectly balanced composition. More than that. This might not even be your goal. When it comes to colour, it all depends on what you are trying to express with it. The colours that work perfectly in one situation won’t serve the purpose in the other, it’s never one size fits all kind of situation.

When choosing a colour, we should always consider the cultural aspect as well. What is the colour of marriage in the Western world, may symbolise death and grief in the East. Yes, I’m speaking about white. Speaking about colour in web design, we should value readability and accessibility over the prettiness of a beautiful colour palette. Colour is a tool that must be used wisely.
Josef Albers, a Bauhaus master and Yale University professor, was famous for teaching revolutionary rigid colour theory. He argued against applying colour mechanically following the rules of colour harmony. Because of the subjective nature of our perception it’s almost impossible to see colour by itself and not interacting with other colours around it.
This only means that it’s good to know rules, but following them without thinking of the context won’t always lead you to perfect results.
CMYK

CMYK is a subtractive colour mixing model used in print on a physical surface: books and magazines, signage and wayfinding, packaging and print advertising. Usage of cyan, magenta, yellow and key/black (CMYK) paints gives a sum of black. This colour combo enables printers to produce a wider variety of colours on paper. So, if your design will be printed, always use the CMYK model.
RGB

RGB is an additive colour mixing model, and it allows you to create colours by mixing red, green and blue light. That is the model used in screens, so it’s important to know while creating the designs that will be perceived on screens and adapt your choice. The physics of the process is simple: the more light you add, the closer you are to the pure white light.
The colour wheel

Make the colour wheel your wheel of fortune. Learning how to use the colour wheel may make you a great favour when you are stuck looking for a suitable colour combination for your design. The first colour wheel was designed by Sir Isaac Newton in 1666. Not that much has changed since then and artists and designers still use is a helpful tool to create harmonious palettes.
Primary, secondary and tertiary colours



The colour wheel consists of three primary colours (red, yellow, and blue), three secondary colours (these are the ones created when primary colours are mixed: green, orange, purple) and six tertiary colours (they are made from primary and secondary colours, such as blue-green or red-violet)
Warm colours

If you draw a line in the centre of the colour wheel the ones on the right will be warm colours (shades of yellow, orange and red). Colour has a temperature, and warm colours are supposed to be more active, creative, energetic and fun.
Cold colours

The ones to the left to the centre will be cold colours (shades of blue, purple and violet).
Cold colours are often used to express calmness, peacefulness and serenity. May sound subjective? It is, but these are the common patterns associated with colours and understanding that will impact the message you are sending with your design.