When I scan a document, it shows up on the preview

Depending on what program you are using to scan, there are usually options to the left of the preview pane where you can choose black/white, greyscale, or color scanning. There should also be an option for selecting resolution. The default resolution is usually set to 400dpi but if an image you scan is large (5x7 or 8x10) you may want to change it to a higher resolution (600 works well).

Options or applications or if you are not dab hand, remove prog and re-install prog!