Function should_color 

pub fn should_color(choice: ColorChoice, is_tty: bool) -> bool

Determine whether ANSI colors should be emitted given the user’s choice and whether stdout is currently a TTY.

This is a pure function that can be tested without side-effects.

choice	is_tty	result
Always	any	true
Never	any	false
Auto	true	true
Auto	false	false