iOS button gradient color

Quick answer：

In iOS, a button's gradient color can be implemented using the `CAGradientLayer` class. This class allows for the creation of a gradient background that can be applied to UI elements like buttons. Developers can define the gradient colors, type (linear or radial), and start and end points. To apply the gradient to a button, you would typically set the gradient layer as the button's background color and adjust its frame to fit the button's size.