Contrast is essential to usability in web design. Complementary colors have a strong impact in the ability of the eye to process image and this principle is applied to designing interfaces in order to retain memory, attention and to generate emotion.

Simple combinations such as the images bellow give us a sense of the role of saturation because not everyone has the same ability to process color. That includes people with disabilities and overall daltonism - which can come in many forms, affecting perception of various and different colors. In a digital space it's important to ensure accessibility to people, avoiding simples mistakes that might make apps and websites hard to read and interact with