GIF image becomes wrong after ImageIO read() and write() operations

I have this code. It simply reads a GIF file, redraws it with background and output to a new GIF file.

The problem is the result file becomes strange. I have no idea why it becomes poor quality. The problem doesn't happen on JPG files. How to fix it?

import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;

public class ImageTest {

    public static void main(String[] args) {
        f();
    }

    private static final String EXTENSION = "gif";
    private static final String FILENAME = "pinkHeart";
    private static final String PATH = "/Users/hieugioi/Downloads/";

    public static void f() {
        File file = new File(PATH + FILENAME + "." + EXTENSION);

        try {
            final BufferedImage originalImage = ImageIO.read(file);

            int imageType = getImageType(originalImage);
            final BufferedImage buff = new BufferedImage(originalImage.getWidth(), originalImage.getHeight(), imageType);
            final Graphics2D g = buff.createGraphics();

            Color backgroundColor = Color.GRAY;
            g.setColor(backgroundColor);
            g.fill(new Rectangle(0, 0, buff.getWidth(), buff.getHeight()));
            g.drawImage(originalImage, null, 0, 0);

            File out = new File(PATH + FILENAME + "Out." + EXTENSION);
            ImageIO.write(buff, EXTENSION, out);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static int getImageType(BufferedImage img) {
        int imageType = img.getType();
        if (imageType == BufferedImage.TYPE_CUSTOM) {
            if (img.getAlphaRaster() != null) {
                imageType = BufferedImage.TYPE_INT_ARGB_PRE;
            } else {
                imageType = BufferedImage.TYPE_INT_RGB;
            }
        } else if (imageType == BufferedImage.TYPE_BYTE_INDEXED && img.getColorModel().hasAlpha()) {
            imageType = BufferedImage.TYPE_INT_ARGB_PRE;
        }
        return imageType;
    }
}

Input image (pinkHeart.gif):

Output image (pinkHeartOut.gif):

Update case 2

Input image (example.gif):

Output image (exampleOut.gif): The output's yellow totally disappears!