But if you didn't know..

Have an iPhone (I am sure android has this but I am not familiar) and want to play with this outside at night?

Go into accessibility and turn on color filters to make your screen red and if you are in a very dark place and your eyes have adjusted turn on the white point adjustment and dim it down as well.

Both can be set as shortcuts to your side button triple click or configured as shortcuts to pin to your Home Screen.

All that said, OP a high contrast mode would be sweet.