How to use semantic colors to help your iOS app adapt to dark mode

Swift version: 5.2

Paul Hudson @twostraws June 3rd 2019

When specifying colors for objects in your views, it’s often easier to use the built-in semantic colors of UIColor rather than specifying our own custom colors that might not look good in both light and dark mode.

For example, when you are coloring a label, use UIColor.label, .secondaryLabel, or similar so that UIKit will automatically make sure it stands out.

For backgrounds you should use UIColor.systemBackground, .secondarySystemBackground, or similar so that when you layer one view over another they don’t appear to become merged.

And when you’re using fixed colors like .red or .blue you should instead use .systemRed or .systemBlue to get a color that will adapt to the user’s trait environment – it will be a lighter red when in dark mode, and a darker red in light mode, rather than the fixed pure red of .red.