How can I convert RGB hex string into UIColor in objective-c?

You're close but colorWithRed:green:blue:alpha: expects values ranging from 0.0 to 1.0, so you need to shift the bits right and divide by 255.0f:

CGFloat red   = ((baseColor1 & 0xFF0000) >> 16) / 255.0f;
CGFloat green = ((baseColor1 & 0x00FF00) >>  8) / 255.0f;
CGFloat blue  =  (baseColor1 & 0x0000FF) / 255.0f;

EDIT - Also NSScanner's scanHexInt will skip past 0x in front of a hex string, but I don't think it will skip the # character in front of your hex string. You can add this line to handle that:

[scanner2 setCharactersToBeSkipped:[NSCharacterSet symbolCharacterSet]]; 

I added a string replacement so it accepts a hex string with or without the #

Possible full code:

+ (UIColor *)colorWithHexString:(NSString *)stringToConvert
{
    NSString *noHashString = [stringToConvert stringByReplacingOccurrencesOfString:@"#" withString:@""]; // remove the #
    NSScanner *scanner = [NSScanner scannerWithString:noHashString];
    [scanner setCharactersToBeSkipped:[NSCharacterSet symbolCharacterSet]]; // remove + and $

    unsigned hex;
    if (![scanner scanHexInt:&hex]) return nil;
    int r = (hex >> 16) & 0xFF;
    int g = (hex >> 8) & 0xFF;
    int b = (hex) & 0xFF;

    return [UIColor colorWithRed:r / 255.0f green:g / 255.0f blue:b / 255.0f alpha:1.0f];
}