can_create_standard_qrcode_graphic_with_custom_finder tests this scenario. However, the finder image used is completely transparent.

Assuming we alter the test with this code:

            var finder = new Bitmap(70, 70);
            using (var g = Graphics.FromImage(finder))
            {
                g.FillRectangle(Brushes.Red, 0, 0, 70, 70);
            }

It would currently produce this image:

With this PR (and the above alteration to the test) it will produce this image:

I suggest the test be altered as shown above, the hash updated, and the PR merged.