Hierarchical scale in art is used to indicate:

Hierarchical scale in art is a technique used to indicate the relative importance of subjects within a composition by varying their size. In this context, larger figures or objects are typically portrayed as more significant or important than smaller ones. This artistic strategy has been employed in various cultures and historical periods to convey social status, power, or divine significance among the depicted figures. For example, in many religious artworks, a central figure such as a deity or a revered saint is often rendered on a larger scale compared to surrounding figures, effectively guiding the viewer's interpretation of the relationships and hierarchies present in the artwork.

Considering the other options, while color usage and texture variety can enhance a composition, they do not specifically denote importance through size. Similarly, the size of the canvas relates to the overall dimensions of the artwork but does not convey the relative importance of subjects within that work. Thus, the correct choice reflects the primary purpose of hierarchical scale in art.