In 1980, Robert Plutchik introduced his very own color wheel of emotions that showed a three-dimensional circumflex model, which described the relations among the concepts of emotions that were portrayed to be analogous to the colors given in the wheel.
The cone's vertical dimension represent intensity while the circle represents the degrees of correspondence among the emotions given in the wheel. As defined by his theory, there are eight primary emotion dimensions that were all indicated by the eight sectors in the model.
Meanwhile, in the exploded model, the blank spaces represent the primary pairs or the dyad of primary emotions. So, it simply implies that when your have this interest and serenity towards a certain subject, you get the feeling of optimism.
Interesting model, isn't?