DeviceLoginScreenHighContrastEnabled

Enable the high contrast accessibility feature on the login screen. If this policy is set to true, the high contrast will always be enabled on the login screen. If this policy is set to false, the high contrast will always be disabled on the login screen. If you set this policy, users cannot change or override it. If this policy is left unset, the high contrast is disabled on the login screen initially but can be enabled by the user anytime.