Monochrome : One colour with varying shades of light and dark
Cool colours together are harmonious.....likewise with warm colours.
Analogous harmony: Any three adjacent colours on the colour wheel.
Complementary harmony: any two colours directly opposite on the colour wheel
You can plan the harmony in a painting as follows :
Monochrome (one colour and tints, shades and tones )
Warm /cool
Analogous
Complementary
But there are more !!