You can set the opacity to a certain UIColor
without creating a new one using the init(red:_,green:_,blue:_,alpha:_)
initializer.
let colorWithAlpha = UIColor.redColor().colorWithAlphaComponent(0.1)
//In Swift Latest Version
_ colorWithAlpha = UIColor.red.withAlphaComponent(0.1)
UIColor * colorWithAlpha = [[UIColor redColor] colorWithAlphaComponent:0.1];