It looks like this whenever off:
While I'd prefer more of a grey background. Do I really have to use a UIImageView?
Here is how I changed the fill color of my iOS7 UISwitch.
First you need to import QuartzCore.
#import <QuartzCore/QuartzCore.h>
Then set the background color and round the UISwitch's corners.
UISwitch *mySwitch = [[UISwitch alloc] initWithFrame:CGRectMake(0.0, 0.0, 51.0, 31.0)];
mySwitch.backgroundColor = [UIColor redColor];
mySwitch.layer.cornerRadius = 16.0; // you must import QuartzCore to do this.
[self addSubview:mySwitch];
This will give you a UISwitch with a custom off (background) color.
Hope this helps someone:)