Color Tint UIButton Image

You must set the image rendering mode to UIImageRenderingModeAlwaysTemplate in order to have the tintColor affect the UIImage. Here is the solution in Swift:

let image = UIImage(named: "image-name")
let button = UIButton()
button.setImage(image?.imageWithRenderingMode(UIImageRenderingMode.AlwaysTemplate), forState: .Normal)
button.tintColor = UIColor.whiteColor()

SWIFT 4x

button.setImage(image.withRenderingMode(UIImage.RenderingMode.alwaysTemplate), for: .normal)
button.tintColor = UIColor.blue

Custom Buttons appear in their respective image colors. Setting the button type to "System" in the storyboard (or to UIButtonTypeSystem in code), will render the button's image with the default tint color.

(tested on iOS9, Xcode 7.3)

As of iOS 7, there is a new method on UIImage to specify the rendering mode. Using the rendering mode UIImageRenderingModeAlwaysTemplate will allow the image color to be controlled by the button's tint color.

Objective-C

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
UIImage *image = [[UIImage imageNamed:@"image_name"] imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
[button setImage:image forState:UIControlStateNormal]; 
button.tintColor = [UIColor redColor];

Swift

let button = UIButton(type: .custom)
let image = UIImage(named: "image_name")?.withRenderingMode(.alwaysTemplate)
button.setImage(image, for: .normal)
button.tintColor = UIColor.red

As Ric already mentioned in his post you can set the render mode in code, you can also do this directly in the image catalog, see attached image below. Just set the Render As to Template Image

Caveat I have had problems with iOS 7 and this approach. So if you use iOS 7 as well you might want to do it in code as well to be sure, as described here.