Please check the second answer of this question on stack overflow

That function doesn't seem to produce the correct ints - not sure what the logic of the return statement is but rgb is already correct here. Try it out and see that it doesn't give the right answer. Honestly it's easier to just write hex constants instead of that function -- 0x0000FF, 0x00FF00

I tried your suggestion, still getting that same black & white 128 barcode. I changed the dimensions of the BitMatrix but still the same result

Hm, I think you don't want transparency, so you need to ensure the top byte is 0xFF, as in 0xFF00FF00 for example.

I tried your solution and the issue still remains
Here's my barcode again:-

I tried every possible solution I found but still no good

Hm, I think you don't want transparency, so you need to ensure the top byte is 0xFF, as in 0xFF00FF00 for example.

Even if I pass 0xFFFFFFFF as both onColor and offColor, still I get the standard black & white barcode, whereas I should get a blank white image

Works fine for me. Are you sure you're reading the right path? Ex:

    Code128Writer writer = new Code128Writer();
    BitMatrix matrix = writer.encode("foobar", BarcodeFormat.CODE_128, 500, 300);
    MatrixToImageConfig conf = new MatrixToImageConfig(0xFF00FF00, 0xFF0000FF);
    BufferedImage qrcode = MatrixToImageWriter.toBufferedImage(matrix, conf);
    File outputfile = new File("/tmp/out.png");
    ImageIO.write(qrcode, "png", outputfile);

It's working now. Thanks a lot man. You're a lifesaver