Dividing the colour wheel in half, we can see that one half contains colours that are warm, active and exciting, whereas the other half is cool, passive and calming.
Warm hues reflect more light than cool hues. Warm hues are sometimes known as advancing colours, while cool hues are known as receding colours.
Colours can broadly be classified as warm or cool according to their yellowness or blueness. However, there are some cool colours that have yellow added and some warm colours that have blue added.
Adding white to a pure colour will dilute its character and render it somewhat colder.