How to ignore sibling UIView's background alpha

I have 3 uiviews. One parent and 2 children. The parent uiview has a sublayer of AVCaptureVideoPreviewLayer which is just a camera view.

With a button clicked, I add my first child uiview which has a backgroundColor.alpha value of 0.5 to basically dim my camera view.

Then I add my second child uiview which is a small rectangular frame (smaller than the first child) and i want this uiview to have a backgroundcolor alpha value of 0. (Transparent) But if i add these two subviews, unless i set the alpha value of the second uiview to a value higher than the first child uiview, it won't show any change. (Guessing probably because the first uiview is darker than the second one)

How can i ignore the first uiview alpha value?