知乎：http://www.zhihu.com/question/33503266?sort=created

http://stackoverflow.com/questions/6207329/how-to-set-hex-color-code-for-background

例子：

[self.view setBackgroundColor: [self colorWithHexString:@"FFFFFF"]]; /* white */

代码：

-(UIColor*)colorWithHexString:(NSString*)hex

{

NSString *cString = [[hex stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] uppercaseString];

// String should be 6 or 8 characters

if ([cString length] < 6) return [UIColor grayColor];

// strip 0X if it appears

if ([cString hasPrefix:@"0X"]) cString = [cString substringFromIndex:2];

if ([cString length] != 6) return  [UIColor grayColor];

// Separate into r, g, b substrings

NSRange range;

range.location = 0;

range.length = 2;

NSString *rString = [cString substringWithRange:range];

range.location = 2;

NSString *gString = [cString substringWithRange:range];

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];

}