The Colours of the Mantra

Syllable	Colour	Purpose	Wisdom
Om	White	Body	Equanimity
Ma	Green	Speech	Activity
Ni	Yellow	Mind	Arising
Pad	Blue	Emotion	Sharing
Me	Red	Learning	Discriminating
Hum	Black	Wisdom	Reflecting

The Purposes are elements of purification and aspects of improvement.
The Wisdoms are aspects of intelligence and actions of mental activity.

The colours and attributions vary from school to school and even between teachers within a school.
This isn't a problem. In Buddhist practice one works with whatever arises.