The other thing you should try is to use the Accessibility Settings in iOS to turn the entire screen red in all apps.
Apple might change this in the future but for now, to set this up, open the Settings app and go to Accessibility > Display & Text Size > Color Filters. Turn Color Filters ON and then slide the Intensity and Hue sliders all the way to the right. This should color the display a deep red.
You can toggle the color filter off and on using the switch on this screen. You can also set up a shortcut to toggle it from the iOS control panel or via a triple tap. To set this up, go to Accessibility > Accessibility Shortcut, and select the Color Filters option.
Even with red film, I recommend using the Accessibility setting. Some blue UI components become invisible with red film if you don't do this.