Function material_spread 

pub fn material_spread(colors: &Colors, ground: AlphaColor<Srgb>) -> f64

How far what shows through a translucent surface of ground may stand off it: MATERIAL_SPREAD, narrowed to what the theme’s inks can afford. Contrast ratios on one side of a ground divide exactly, so ink with ratio r on the ground keeps r / spread on the band’s far end; the spread is the least of r / floor over the three ink tiers (body text for primary and secondary, large text for tertiary, AAA text on a high-contrast palette), never below 1 (an opaque surface).