UIColor+HSBFunctions.h

@interface UIColor (HSBFunctions)

- (UIColor *)lightenedColorByPercent:(CGFloat)percent;
- (UIColor *)darkenedColorByPercent:(CGFloat)percent;

@end

UIColor+HSBFunctions.m

#import "UIColor+HSBFunctions.h"

@implementation UIColor (HSBFunctions)

- (UIColor *)lightenedColorByPercent:(CGFloat)percent
{
    CGFloat hue, saturation, brightness, alpha;
    [self getHue:&hue saturation:&saturation brightness:&brightness alpha:&alpha];
    
    return [UIColor colorWithHue:hue saturation:saturation brightness:(brightness + 1.0 * (percent / 100.0)) alpha:alpha];
}

- (UIColor *)darkenedColorByPercent:(CGFloat)percent
{
    CGFloat hue, saturation, brightness, alpha;
    [self getHue:&hue saturation:&saturation brightness:&brightness alpha:&alpha];
    
    return [UIColor colorWithHue:hue saturation:saturation brightness:(brightness - 1.0 * (percent / 100.0)) alpha:alpha];
}

@end