A macOS app for quick access to WCAG color contrast ratios → https://itunes.apple.com/de/app/contrast-color-accessibility/id1254981365?l=en&mt=12

… a specialized remote screen viewing application intended as a tool to help designers create graphics for mobile applications, it has also proven to be useful for creating quick and dirty simulations, demos, and experience prototypes.

… makes it easy to quickly create high-quality custom controls for your iOS apps, Mac apps and for the web.