// If you want to get black text on a white background,
// there is only one way out - to cut it out of the background
Circle()
    .fill(.white)
    .frame(width: 20, height: 20, alignment: .center)
    .mask(
        ZStack {
            Circle()
                .fill(Color.white)

            Text(model.formattedDayNumber)
                .font(.system(size: 9, weight: .bold))
                .foregroundColor(.black)

        }
        .compositingGroup()
        .luminanceToAlpha()
    )