Use something like this (Not compiler checked)

NSMutableAttributedString *string = [[NSMutableAttributedString alloc]initWithString:self.text.text];
NSRange range=[self.myLabel.text rangeOfString:texts[sliderValue]]; //myLabel is the outlet from where you will get the text, it can be same or different

NSArray *colors=@[[UIColor redColor],
                  [UIColor redColor],
                  [UIColor yellowColor],
                  [UIColor greenColor]
                 ];

[string addAttribute:NSForegroundColorAttributeName 
               value:colors[sliderValue] 
               range:range];           

[self.scanLabel setAttributedText:texts[sliderValue]];