Creates a color object that has the same color space and component values as the receiver, but has the specified alpha component.
- iOS 2.0+
- tvOS 9.0+
- watchOS 2.0+
The opacity value of the new color object, specified as a value from 0.0 to 1.0. Alpha values below 0.0 are interpreted as 0.0, and values above 1.0 are interpreted as 1.0
A subclass with explicit opacity components should override this method to return a color with the specified alpha.