Objective-c UIColor category get color from hex string.

UIColor+HexString.h

//
//  UIColor+HexString.h
//  DemoMapviewScrollView
//
//  Created by ThinhPhan on 12/18/14.
//  Copyright (c) 2014 Gennova. All rights reserved.
//

#import <UIKit/UIKit.h>

@interface UIColor (HexString)

/*!
 *  @author Thinh Phan, 14-12-18 16:12:14
 *
 *  @ref http://stackoverflow.com/a/3805354
 *
 *  @brief  Change from hex string to UIColor
 *
 *  @param hexString string format "#abc", "#abcdef31" or "RRGGBB"
 *
 *  @return UIColor object.
 */
+ (UIColor *)colorFromHexString:(NSString *)hexString;

/*!
 *  @author Thinh Phan, 14-12-18 16:12:12
 *
 *  @brief  Convert from hex string to UIColor object.
 *
 *  @param hexString string format : #RBG, #ARGB ##RRGGBB or #AARRGGBB.
 *
 *  @return UIColor object.
 */
+ (UIColor *)colorWithHexString:(NSString *)hexString;
@end

UIColor+HexString.m

//
//  UIColor+HexString.m
//  DemoMapviewScrollView
//
//  Follow http://stackoverflow.com/a/7180905
//  Created by ThinhPhan on 12/18/14.
//  Copyright (c) 2014 Gennova. All rights reserved.
//

#import "UIColor+HexString.h"

@implementation UIColor (HexString)

+ (UIColor *)colorFromHexString:(NSString *)hexString {
    NSString *cleanString = [hexString stringByReplacingOccurrencesOfString:@"#" withString:@""];
    if([cleanString length] == 3) {
        cleanString = [NSString stringWithFormat:@"%@%@%@%@%@%@",
                       [cleanString substringWithRange:NSMakeRange(0, 1)],[cleanString substringWithRange:NSMakeRange(0, 1)],
                       [cleanString substringWithRange:NSMakeRange(1, 1)],[cleanString substringWithRange:NSMakeRange(1, 1)],
                       [cleanString substringWithRange:NSMakeRange(2, 1)],[cleanString substringWithRange:NSMakeRange(2, 1)]];
    }
    if([cleanString length] == 6) {
        cleanString = [cleanString stringByAppendingString:@"ff"];
    }
    
    unsigned int baseValue;
    [[NSScanner scannerWithString:cleanString] scanHexInt:&baseValue];
    
    float red   = ((baseValue >> 24) & 0xFF)/255.0f;
    float green = ((baseValue >> 16) & 0xFF)/255.0f;
    float blue  = ((baseValue >> 8)  & 0xFF)/255.0f;
    float alpha = ((baseValue >> 0)  & 0xFF)/255.0f;
    
    return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}

+ (UIColor *)colorWithHexString:(NSString *)hexString {
    NSString *colorString = [[hexString stringByReplacingOccurrencesOfString: @"#" withString: @""] uppercaseString];
    CGFloat alpha, red, blue, green;
    
    switch ([colorString length]) {
        case 3: // #RGB
            alpha = 1.0f;
            red   = [self colorComponentFrom: colorString start: 0 length: 1];
            green = [self colorComponentFrom: colorString start: 1 length: 1];
            blue  = [self colorComponentFrom: colorString start: 2 length: 1];
            break;
        case 4: // #ARGB
            alpha = [self colorComponentFrom: colorString start: 0 length: 1];
            red   = [self colorComponentFrom: colorString start: 1 length: 1];
            green = [self colorComponentFrom: colorString start: 2 length: 1];
            blue  = [self colorComponentFrom: colorString start: 3 length: 1];
            break;
        case 6: // #RRGGBB
            alpha = 1.0f;
            red   = [self colorComponentFrom: colorString start: 0 length: 2];
            green = [self colorComponentFrom: colorString start: 2 length: 2];
            blue  = [self colorComponentFrom: colorString start: 4 length: 2];
            break;
        case 8: // #AARRGGBB
            alpha = [self colorComponentFrom: colorString start: 0 length: 2];
            red   = [self colorComponentFrom: colorString start: 2 length: 2];
            green = [self colorComponentFrom: colorString start: 4 length: 2];
            blue  = [self colorComponentFrom: colorString start: 6 length: 2];
            break;
        default:
            [NSException raise:@"Invalid color value"
                        format: @"Color value %@ is invalid.  It should be a hex value of the form #RBG, #ARGB, #RRGGBB, or #AARRGGBB", hexString];
            break;
    }
    return [UIColor colorWithRed: red green: green blue: blue alpha: alpha];
}

#pragma mark - Helper Methods
+ (CGFloat)colorComponentFrom:(NSString *)string start:(NSUInteger)start length:(NSUInteger)length {
    NSString *substring = [string substringWithRange: NSMakeRange(start, length)];
    NSString *fullHex = length == 2 ? substring : [NSString stringWithFormat: @"%@%@", substring, substring];
    unsigned hexComponent;
    [[NSScanner scannerWithString: fullHex] scanHexInt: &hexComponent];
    return hexComponent / 255.0;
}
@end