Not sure how I would use that. Do you mean 2 custom colors to change both the default orange and blue? I can perfectly distinguish them when they're on a bolder shape (🟠🔵), it's just a lot harder (or sometimes impossible) on a thin line/symbol.

Again, the most efficient way to handle it would be to have a different style for the selected arrow (bolder, bigger, underlined or circled for example), on top of its color. It would then work as well in bedtime mode (b/w and low brightness) for everyone, not just for color blind people :)

I think bedtime mode activates by default on newer Android devices after 10pm when the phone is charging. That's how mine (OnePlus) was set up.

I see my initial reply was upvoted about 30 times. Statistically speaking, I don't think these would be only from color blind people