十六进制颜色

建议生成UIColor的分类使用，如下：

.h

@interface UIColor (HSF_HexString)

+ (UIColor*)colorWithHexString:(NSString*)color;

+ (UIColor*)colorWithHexString:(NSString*)color alpha:(CGFloat)alpha;

@end

.m

@implementation UIColor (HSF_HexString)

+ (UIColor *)colorWithHexString:(NSString *)color {
    NSString *cString = [[color stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] uppercaseString];
    
    // String should be 6 or 8 characters
    if ([cString length] < 6) {
        return [UIColor clearColor];
    }
    
    // strip 0X if it appears
    if ([cString hasPrefix:@"0X"])
        cString = [cString substringFromIndex:2];
    if ([cString hasPrefix:@"#"])
        cString = [cString substringFromIndex:1];
    if ([cString length] != 6)
        return [UIColor clearColor];
    
    // Separate into r, g, b substrings
    NSRange range;
    range.location = 0;
    range.length = 2;
    
    //r
    NSString *rString = [cString substringWithRange:range];
    
    //g
    range.location = 2;
    NSString *gString = [cString substringWithRange:range];
    
    //b
    range.location = 4;
    NSString *bString = [cString substringWithRange:range];
    
    // Scan values
    unsigned int r, g, b;
    [[NSScanner scannerWithString:rString] scanHexInt:&r];
    [[NSScanner scannerWithString:gString] scanHexInt:&g];
    [[NSScanner scannerWithString:bString] scanHexInt:&b];
    
    return [UIColor colorWithRed:((float) r / 255.0f) green:((float) g / 255.0f) blue:((float) b / 255.0f) alpha:1.0f];
}

+ (UIColor*) colorWithHexString:(NSString*)color alpha:(CGFloat)alpha {
    return [[self colorWithHexString:color] colorWithAlphaComponent:alpha];
}

@end