Function terminal_light::luma

pub fn luma() -> Result<f32, TlError>

Try to return the “luma” value of the terminal’s background, characterizing the “light” of the color, going from 0 (black) to 1 (white).

You can say a terminal is “dark” when the luma is below 0.2 and “light” when it’s over 0.9. If you need to choose a pivot between “rather dark” and “rather light” then 0.6 should do.