define UIColorFromRGB(rgbValue) [UIColor colorWithRed:((float)((rgbValue & 0xFF0000) >> 16))/255.0 green:((float)((rgbValue &0xFF00) >>8))/255.0 blue:((float)(rgbValue &0xFF))/255.0 alpha:1.0]；

使用：
self.btnWork.backgroundColor =UIColorFromRGB(0x1874de);

2.将16进制字符串转换成uicolor
注：参数值不带＃号
// 将16进制字符串转换成uicolor
-(UIColor)toUIColorByStr:(NSString)colorStr{
NSString *cString = [[colorStr stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] uppercaseString];

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

// 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];

}

//3.将UIColor转换成16进制字符串
// 注意转换出来的字符串不带＃号
-(NSString)toStrByUIColor:(UIColor)color{
CGFloat r, g, b, a;

    [color getRed:&r green:&g blue:&b alpha:&a];

    int rgb = (int) (r * 255.0f)<<16 | (int) (g * 255.0f)<<8 | (int) (b * 255.0f)<<0;

NSString  *rgbStr=[NSString stringWithFormat:@"#%06x", rgb];
return rgbStr;

}