When defining primaries, the goal is often to leave as many real colors in gamut as possible. Since the region of real colors is not a triangle (see illustration), it is not possible to pick three real colors that span the whole region. The gamut can be increased by selecting more than three real primary colors, but since the region of real colors is not a polygon, there will always be some colors at the edge left out. Therefore, one selects colors outside of the region of real colors as primary colors; in other words, imaginary or fictitious primary colors. Mathematically, the gamut created in this way contains so-called imaginary or fictitious colors.
