To access the UI colors settings, press Escape then choose Settings. On the top row choose Accessibility then click on Color blindness on the left. You can change your UI colors by clicking on the Customize UI colors button.

After clicking on the Customize UI colors button, a popup window opens with four drop-down menus, where you can choose your desired colors for your enemies, friendlies, groupmates and alerts. You can preview your changes on the right, but if you're unsure you can view your settings in-game, by clicking on the Full preview button.