Repetition’s impact is a matter of brain chemistry. The more our brains see a piece of information, the greater we perceive its importance to be. We are highly susceptible to the effect of repetition.
Na, na, na, na, anybody?
Consistency unites information, making its impact stronger.
Contrast, however, can be equally striking. It is the most common tool for a designer to control the attention of the viewer. Strong contrasts can display boldness, while minimal contrast can convey the opposite.