The Colour-Change Charm is a standard piece of magic taught in the Charms curriculum at Hogwarts School of Witchcraft and Wizardry. Its primary function is to alter the hue of the target. The charm is most notably featured as a component of the practical Charms examination for the Ordinary Wizarding Level (O.W.L.) exams. During his O.W.L. in 1996, Harry Potter was required to use this spell to turn a rat orange. He performed the Charm successfully, earning a tick of approval from the examiner, Professor Tofty. Prior to the exam, Hermione Granger mentioned practicing the spell, noting that she had made an orange turn blue and that it hadn't been a very difficult spell to master. By the Nastily Exhausting Wizarding Test (N.E.W.T.) level, students are expected to perform more advanced versions of this magic. In their sixth-year Charms class with Professor Flitwick, students practiced non-verbal spellcasting, and Hermione Granger successfully performed a non-verbal Colour-Change Charm on a leaf, earning praise from her teacher.
The verbal version of the Colour-Change Charm is considered standard curriculum for fifth-year students preparing for their O.W.L.s, suggesting it is of average difficulty. The ability to perform the spell non-verbally is a mark of a more advanced and skillful wizard, as practiced in N.E.W.T.-level classes. While no specific counter-spell is mentioned in the novels, it is likely that the effects can be reversed by a general-purpose counter-spell such as the General Counter-Spell (Finite Incantatem).
The incantation Colovaria, used in the video games, is a portmanteau derived from Latin. It likely combines the Latin word color, meaning “colour,” with variare, meaning “to change” or “to vary.” The incantation can thus be literally translated as “to change colour.”