You can use -[UIButton setTitleColor:forState:]
to do this.
Example:
Objective-C
[buttonName setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
Swift 2
buttonName.setTitleColor(UIColor.blackColor(), forState: .Normal)
Swift 3
buttonName.setTitleColor(UIColor.white, for: .normal)
Thanks to richardchildan