Colovaria is a charm used to change the colour of something; it can also be used to change the style of one's hair, in a similar manner to the transfiguration spell Multicorfors.
Harry Potter used this spell sometime from 1991 to 1995, to turn his hair orange.
The incantation for this charm comes from the English words colour (the visual perceptual property corresponding in humans to the categories called red, blue, yellow, green and others) and vary (to make or cause changes in the characteristics or attributes of; modify or alter).
This may be the incantation for the Colour Change Charm, as it is also a charm used to change the colour of something.
It is also probably related to Multicorfors, a transfiguration spell which alters the colour and style of a person's hair, and Crinus Muto, which is a charm with the same effect as Multicorfors.