一些小知識點（五）未完待續。。。

1. RGB顏色與十六進制顏色轉碼工具中此處的RGB值爲SRGB而非普通RGB
   工具地址：http://tool.css-js.com/rgba.html
   十六進制與十進制轉換：http://tool.oschina.net/hexconvert/
   轉換代碼：

#define CTColorHex(c) [UIColor colorWithRed:((c>>16)&0xFF)/255.0 green:((c>>8)&0xFF)/255.0 blue:((c)&0xFF)/255.0 alpha:1.0]
#define CTColorHexA(c,a) [UIColor colorWithRed:((c>>16)&0xFF)/255.0 green:((c>>8)&0xFF)/255.0 blue:((c)&0xFF)/255.0 alpha:(a)]

CTColorHex(0x006800)
CTColorHexA(0x006800,0.2)

上面的十六進制數先轉換成2進制數再右移
&0xFF的話還等於自己（&運算符 只有1和1與得1 其他都0）
這裏得到十六進制數直接／255.0 轉換成10進制

16進制的00，68，00分別對應2進制的0000，0110 1000，0000
2進制轉換成10進制 01101000 即8+32+64 ＝ 104

所以16進制的68=10進制的104

[UIColor colorWithHexString:@"#666666"];

+ (UIColor *)colorWithHexString:(NSString *)stringToConvert
{
    NSString *cString = [[stringToConvert stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] uppercaseString];

    if ([cString length] < 6)
        return DEFAULT_VOID_COLOR;
    if ([cString hasPrefix:@"#"])
        cString = [cString substringFromIndex:1];
    if ([cString length] != 6)
        return DEFAULT_VOID_COLOR;

    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];


    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];
}

可以試驗一下，然後對比工具轉換的值，然後用Mac的數碼測色計查看，此RGB值爲以sRGB顯示的。