Variety is a principle of design that deals with diversity or contrast of art elements. Variety helps the artist project or invoke a feeling or emotion.
An example is Juan Luna's painting, the Spoliarium. In the painting, it is noticable that all the the "light source" is focused on the dead gladiator being dragged away form the arena. The art style of Spoliarium is heavily influenced by the Baroque period artist Rembrandt. The style of Rembrandt uses a black background to emphasise the subject matter by using contrast of a light source and darkness.
Elements of art and principle of arts:
Variety is the principle of art that adds interest to an artwork. Variety works through juxtaposition and contrast. When an artist places different visual elements next to one another, he/she is using variety. Straight lines next to curvy lines add variety.