The background is black in your image because you are not giving any pixels a value except those in the rectangles. The BufferedImage
is starting out with every pixel having RGB of (0, 0, 0), which is black. To give the entire image a white background, simply fill the entire rectangle that is the image with white.
BufferedImage image = new BufferedImage(100, 100, BufferedImage.TYPE_INT_RGB);
g = image.createGraphics(); // not sure on this line, but this seems more right
g.setColor(Color.white);
g.fillRect(0, 0, 100, 100); // give the whole image a white background
g.setColor(Color.blue);
for( ..... ){
g.fillRect(X , Y, width , height );
....
}
Note that my answer is about writing the image to a file with a white background, not about drawing to the JFrame with a black background. I'm not entirely sure which one you wanted.