Definitions for "colouring"
Whilst the earliest illustrations were published in black and white, watercolour was added by hand to embellish many important early works, especially with regards the cartouche of a map destined for presentation to the person who had funded the voyage of discovery depicted. Later, a more economical method of printing in colour was devised.
oxides Various metal oxides when painted on or mixed into a glaze give different colours. Copper oxide gives green, manganese oxide gives brown or purple, iron oxide gives brown or green, cobalt oxide gives blue.
Keywords:  vertex, graph, assigned
an assignment of colours to a graph so that every vertex is assigned a colour
same as coloring.
a digestible substance used to give color to food; "food color made from vegetable dyes"
a visual attribute of things that results from the light they emit or transmit or reflect; "a white color is made up of many different wavelengths of light"