How can I change image tintColor

Try to generate new image for yourself

UIImage *newImage = [_sketchImageView.image imageWithRenderingMode:UIImageRenderingModeAlwaysTemplate];
UIGraphicsBeginImageContextWithOptions(image.size, NO, newImage.scale);
[yourTintColor set];
[newImage drawInRect:CGRectMake(0, 0, image.size.width, newImage.size.height)];
newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

_sketchImageView.image = newImage;

And use it.

Good luck

======= UPDATE =======

This solution will only change color of all pixel's image.

Example: we have a book image: http://pngimg.com/upload/book_PNG2113.png

And after running above code (exp: TintColor is RED). We have:

SO: how your image is depends on how you designed it

In Swift you can use this extension: [Based on @VietHung's objective-c solution]

Swift 5:

extension UIImage {
      func imageWithColor(color: UIColor) -> UIImage? {
        var image = withRenderingMode(.alwaysTemplate)
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        color.set()
        image.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
        image = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        return image
    }
}

Previous Swift version:

extension UIImage {
    func imageWithColor(color: UIColor) -> UIImage? {
        var image = imageWithRenderingMode(.AlwaysTemplate)
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        color.set()
        image.drawInRect(CGRect(x: 0, y: 0, width: size.width, height: size.height))
        image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }
}