This document discusses hair colouring and provides information about determining a client's warm or cool undertones, using a colour wheel and shade charts, and some basic rules of hair colouring. It explains that the colour wheel can help colourists understand how colours work together and neutralize each other. It also notes that determining if a client is warm or cool-toned is important for colour selection and can be assessed by looking at their skin, eye colour, and preferred makeup and clothing shades. Warm and cool hair colour examples are provided.