Select the image/bitmap Layer.
Go to the Property Inspector > Filters > Adjust Colors > Saturation.
Drag the Saturation slider all the way to -100.
This is a mere workaround as Fw does not handle/deal in Color Spaces.
Select the bitmap object/layer > go to menu Commands > Creative > Convert to grayscale
This will automatically apply a filter which will make the image black and white
(You'll see the filter appear in the Property Inspector, in Live Filters area)
Hope this helps, too!