Theorically to make a black & white mosaic you need a collection of Black & White images and the original image to use for the mosaic must be a Black & White Image. But there are some shortcuts and experiments you can do without this needs.
First of all find a Black&White image. But if you don’t have then with any common graphis program you can convert your color image into a Black&White image.
Now you can use the Black&White image even with a color Image Collection. You will be surprised by the results. Maybe you can use a somewhat higher value, like 18% for the parameter “How much can I modify every tile”.
Another solution is to let work AndreaMosaic as if you have a grayscale image collection. For to do this follow this instruction: