Your phone is designed to be distracting❷. Using bright colors is one way it steals your attention; notifications❼ are an alarming red❹ and app icons are rarely black and white.
The Center for Humane Technology❹ suggests turning your phone grayscale❷ to counteract this.
iPhone:Settings → General → Accessibility → Accessibility Shortcut → Color FiltersThis allows you to switch between grayscale and full color by triple clicking the home button.
Android: settings differ between devices