This appears to be a typo of "colour" (the UK spelling of the word color).
It depends where you live. In the USA and Canada, people say color, and in the UK and any other English-speaking places(usually) it is colour. Just the culture.
That is the correct US spelling of "gray matter" (brain tissue). The predominant UK and Canadian spelling of the color is "grey."
You spell the color blue like so- BLUE.
In British English, the correct spellings are colour and favourite."Green is my favourite colour".In American English, the correct spellings are color and favorite."That color is not my favorite".
available
Anaesthetic.
LITRE.
The American spelling is color.
The spelling "color" is the American English variation, while "colour" is the British English version. This difference in spelling stems from historical linguistic developments and the influence of various languages on English over time.
The US spellings are "color" and "colored" as opposed to the UK spellings colour/coloured)
Nothing, except the nationality of the writer. Americans spell it color and generally, British people spell it colour, with a U.