Function face_colors 

pub fn face_colors(
    theme: &Theme,
    role: ButtonRole,
    interact: Interaction,
) -> (AlphaColor<Srgb>, Option<AlphaColor<Srgb>>, AlphaColor<Srgb>)

The colours of role in interact, the one source for the retained and immediate-mode painters; edge is None where the fill defines the shape or there is no face.