http://stackoverflow.com/questions/7542950/how-do-you-change-uibutton-image-alpha-on-disabled-state#22089729

UIImage+Tint.h

#import <UIKit/UIKit.h>

@interface UIImage (Tint)

- (UIImage *)translucentImageWithAlpha:(CGFloat)alpha;

- (UIImage *)tintedGradientImageWithColor:(UIColor *)tintColor;
- (UIImage *)tintedImageWithColor:(UIColor *)tintColor;

@end

UIImage+Tint.m

#import "UIImage+Tint.h"

@implementation UIImage (Tint)

#pragma mark - Public methods

// http://stackoverflow.com/a/7543459/1367622
- (UIImage *)translucentImageWithAlpha:(CGFloat)alpha
{
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0);
    CGRect bounds = CGRectMake(0, 0, self.size.width, self.size.height);
    [self drawInRect:bounds blendMode:kCGBlendModeScreen alpha:alpha];

    UIImage * translucentImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return translucentImage;
}

- (UIImage *)tintedGradientImageWithColor:(UIColor *)tintColor
{
    return [self tintedImageWithColor:tintColor blendingMode:kCGBlendModeOverlay];
}

- (UIImage *)tintedImageWithColor:(UIColor *)tintColor
{
    return [self tintedImageWithColor:tintColor blendingMode:kCGBlendModeDestinationIn];
}

#pragma mark - Private methods

// http://robots.thoughtbot.com/designing-for-ios-blending-modes
- (UIImage *)tintedImageWithColor:(UIColor *)tintColor blendingMode:(CGBlendMode)blendMode
{
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0f);
    [tintColor setFill];
    CGRect bounds = CGRectMake(0, 0, self.size.width, self.size.height);
    UIRectFill(bounds);
    [self drawInRect:bounds blendMode:blendMode alpha:1.0f];

    // if blend mode was overlay, restore image alpha
    if (blendMode != kCGBlendModeDestinationIn)
        [self drawInRect:bounds blendMode:kCGBlendModeDestinationIn alpha:1.0];

    UIImage * tintedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return tintedImage;
}

@end