UIButton をグラデーションにする ref: http://qiita.com/items/200cafdf1ee381453f1a

IKGrayButton.h

//
//  IKGrayButton.h
//  Ikuzo
//
//  Created by Haruyuki Seki on 3/28/13.
//

#import <UIKit/UIKit.h>

@interface IKGrayButton : UIButton

@end

objective-c

//
//  IKGrayButton.m
//  Ikuzo
//
//  Created by Haruyuki Seki on 3/28/13.
//

#import "IKGrayButton.h"
#import "UIColor+Utilities.h"
#import <QuartzCore/QuartzCore.h>

@implementation IKGrayButton

- (id)initWithCoder:(NSCoder *)aDecoder
{
    self = [super initWithCoder:aDecoder];
    [self setTitleColor:[UIColor hexToUIColor:@"666666" alpha:1.0f] forState:UIControlStateNormal];
    return self;
}
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect
{

    CAGradientLayer *gradient = [CAGradientLayer layer];
    gradient.frame = self.bounds;
    gradient.colors = @[
                        (id)[[UIColor hexToUIColor: @"fdfbf3" alpha: 1.0] CGColor],
                        (id)[[UIColor hexToUIColor: @"d7d6d1" alpha: 1.0] CGColor]
                        ];
    gradient.cornerRadius = 3;
    gradient.borderColor =[[UIColor hexToUIColor:@"cccccc" alpha:1.0] CGColor];
    gradient.borderWidth = 1.0f;
    [self.layer insertSublayer: gradient atIndex: 0];

}

@end

UIColor+Utilities.m

//
//  UIColor+Utilities.m
//  Ikuzo
//
//  Created by Haruyuki Seki on 3/28/13.
//

#import "UIColor+Utilities.h"

@implementation UIColor (Utilities)
+ (UIColor*) hexToUIColor: (NSString *)hex alpha: (CGFloat)a
{
    NSScanner *colorScanner = [NSScanner scannerWithString: hex];
    unsigned int color;
    [colorScanner scanHexInt: &color];
    CGFloat r = ((color & 0xFF0000) >> 16) / 255.0f;
    CGFloat g = ((color & 0x00FF00) >> 8) / 255.0f;
    CGFloat b =  (color & 0x0000FF) / 255.0f;
    return [UIColor colorWithRed: r green: g blue: b alpha: a];
}

@end