What's the meaning of the phrase 'Colour up'?
To colour up is to blush or turn red in the face.
What's the origin of the phrase 'Colour up'?
It's not an especially old phrase and isn't seen in print until 1836, in Frederick Marryat's Japhet in Search of a Father:
"Her ladyship coloured up with rage."
The verb colour, meaning to blush, was used earlier, as in this example from Samuel Johnson's Dictionary of the English Language, 1755:
"To colour, to blush. A low word, only used in conversation."