The documentation says the clearColor's grayscale and alpha = 0. What does that actually mean? Is it just a color to match whatever the background is?
Answer
clearColor is exactly what it says, its clear, so whatever the color is of the view behind the clearColor view, will show through. Think of it as being like clear glass, it is see through e.g. has an alpha value of 0 (zero).
So, say your window background is Red and the background of the view you place on on top of it is clearColor then you will see Red...