BYOND isn't advanced enough to do that kind of manipulation. In order to do this you'll have to either use invisibility or mess about with /image objects. Both require you to redraw your icons in the black & white format.

If you really wish to do this, I recommend using Irfanview to turn the images into greyscale and then just import them into a DMI file. You can do this for quick & easy black 'n white icons although it will take time.