Black and white (or monochrome, or 2 colors) is not the same as grayscale, which typically includes black, white, and various shades of gray. When the system converts a color or grayscale image to black and white, dark colors are changed to black and light colors are changed to white.
The Invoice modules always extractdata from a black and white image, regardless of the number of colors on the original document or how it is displayed on your screen.
If the displayed image is grayscale or color, you can adjust the display to see the black and white image that the system is using. You do this in the dialog.
You can also adjust grayscale to black and white conversion settings on invoices.