Low contrast is a very common problem, not just for permanent visual impairments but also for situational ones, such as playing in direct sunlight or on a device that is in power saving mode.
A high contrast option can be either a post-processing filter (eg. gamma), a set of alternative assets, with for example lighter backgrounds and darker characters than the default, or even something as simple as a tintable layer sitting between the foreground and background – something that took the developer of Epic Eric around 1.5 hours to implement.
The Xbox SDK includes an API to query to find out if a player has their console UI set to high contrast mode; if so, you can enable your own high contrast mode by default.
Best practice example: Uncharted 4
Best practice example: Destiny 2
Best practice example: Joylancer
Best practice example: Street Fighter IV
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Best practice example: My Ex Boyfriend the Space Tyrant
Best practice example: Epic Eric
More information: Accessibility functionality available in the Xbox SDK (video)