Objective-C
mySwitch.backgroundColor = [UIColor yellowColor];
[mySwitch setBackgroundColor: [UIColor yellowColor]];
mySwitch.backgroundColor =[UIColor colorWithRed:255/255.0 green:0/255.0 blue:0/255.0 alpha:1.0];
mySwitch.backgroundColor= [UIColor colorWithWhite: 0.5 alpha: 1.0];
mySwitch.backgroundColor=[UIColor colorWithHue: 0.4 saturation: 0.3 brightness:0.7 alpha: 1.0];
Swift
mySwitch.backgroundColor = UIColor.yellow
mySwitch.backgroundColor = UIColor(red: 255.0/255, green: 0.0/255, blue: 0.0/255, alpha: 1.0)
mySwitch.backgroundColor = UIColor(white: 0.5, alpha: 1.0)
mySwitch.backgroundColor = UIColor(hue: 0.4,saturation: 0.3,brightness: 0.7,alpha: 1.0)