Multi-colored Shadow Swift
Thanks to @Josh Homann for pointing me in the right direction, but the answer was actually much more complex.
The first (bottom) UIView in the hierarchy should have a plain white background and be pinned to the edges of the screen.
The next view should be a UIImageView with an alpha of 0.75.
Then you should add a UIVisualEffectView with the same dimensions as the first view.
Finally, add another UIImageView that is the same size as the first UIImageView.
Your IB hierarchy should look similar to this:
The final result is this: