ios – Shade in UISwitch monitor

I’ve a UISwitch to which I’m customising the thumb and monitor colour.

if (locationTrackingSwitch.On)
    locationTrackingSwitch.ThumbTintColor = FromHEX(theme.colorInput);
else
    locationTrackingSwitch.ThumbTintColor = FromHEX(theme.colorButton);
locationTrackingSwitch.Layer.CornerRadius = (nfloat)(locationTrackingSwitch.Body.Peak / 2.0);
locationTrackingSwitch.BackgroundColor = UIColor.Black; //FromHEX(theme.colorInput);
locationTrackingSwitch.OnTintColor = FromHEX(theme.colorButton);

If the background colour is Black, it reveals black within the monitor like in pic

But when the background colour is white as in

locationTrackingSwitch.BackgroundColor = UIColor.White; 
//FromHEX(theme.colorInput);` 

It reveals grey color monitor as a substitute of white as in

.

I’m not understanding why the white colour shouldn’t be seen. It really works high quality with every other colour. Additionally, the identical white colour reveals high quality with the thumb within the “On” state.
(theme.ColorInput is white colour, “#ffffff”)