rewrite this but keep the message and idea: When implementing an application interface, we should specify background and foreground colors with sufficient color contrast.

A “contrast ratio” is a computation when viewing an interface on devices in extreme lighting conditions. This ratio ranges from 1 to 21 (often written as 1:1 to 21:1), where increasing numbers mean higher contrast. There are many tools available for computing the contrast ratio of two neighboring colors, such as this [color contrast ratio calculator](http://leaverou.github.io/contrast-ratio/).