Function worst_grounds 

pub fn worst_grounds(
    colors: &Colors,
    finishes: &RoleFinishes,
    role: SurfaceRole,
) -> [AlphaColor<Srgb>; 2]

What a surface of role can look like at its darkest and its lightest under finishes, over any backdrop: the role’s ground when it is opaque; the band around it (material_band) when it shows a blurred backdrop; and for a translucent control, which is never blurred, its ground at its tint over the darkest and lightest window it can stand on.