iOS and Xcode provide a wide variety of tools and options to deal with color contrast ratios. From system colors, that automatically support Increase Contrast, to high contrast color and asset variants, and even a built-in contrast calculator.

If you are using SwiftUI to build your apps, there is a fairly basic but very useful Accessibility Inspector built right there in the Inspectors Panel, on the right side of Xcode.

If you use Interface Builder to build your app’s layout, there are some basic accessibility attributes that can be configured from there. They can be found in the Identity Inspector in the right-side panel in Xcode.

There is an Environment Overrides panel in the toolbar on top of Xcode's Debug Area. It allows you to select some of the most common accessibility options and Dynamic Type sizes, like in the Accessibility Inspector, plus select dark/light mode.

Xcode has a built-in tool to help you develop more accessible apps, the Accessibility Inspector. You can find it in the Developer Tool set in the Xcode menu. It has three main functionalities: inspect, audit and settings.