1.  colouring(n = noun.food) coloring, food color, food coloring, food colour, food colouring - a digestible substance used to give color to food; "food color made from vegetable dyes"
is a kind of food product, foodstuff
Derived form verb colour₅

2.  colouring(n = noun.attribute) color, coloring, colour - 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"
is a kind of visual property
has particulars: primary color, primary colour, heather, heather mixture, mottle, shade, tincture, tint, tone, chromatic color, chromatic colour, spectral color, spectral colour, achromatic color, achromatic colour, coloration, colouration, complexion, skin color, skin colour, dithered color, dithered colour, nonsolid color, nonsolid colour
Derived form verb colour₅

3.  colouring(n = noun.act) coloring - the act or process of changing the color of something;
is a kind of change of color
has particulars: tinting, hair coloring, dyeing
Derived form verb colour₆

   same as coloring. [WordNet 1.5]

colouring, n. (US coloring)
1 the process of or skill in using colour(s).
2 the style in which a thing is coloured, or in which an artist uses colour.
3 facial complexion.

colouring material, food colouring