At first glance a full colour wall can appear daunting – so many colours to choose from! The best thing you can do is to stop and think "there are only three colours" – blue, red and yellow. These are your Primary Colours.
Every paint colour in a colour wall has come from a mixture of these three. To understand what colours result from mixing the Primary Colours you should refer to a colour wheel like the one below.
Mixing two Primary Colours together results in a Secondary Colour which can be found between the Primary Colours used to create it - for example, adding red and blue together gives you purple. In between the Secondary Colours you will find the Tertiary Colours that come mixing two Secondary Colours.
Colours such as white, black, beige, ivory and grey are called Neutral Colours as they appear to be "without" colour, though all neutrals except white and grey do come from the colour wheel.