You can ask them to do whatever you want but that doesn’t mean they’ll be able to do it. Not every shoe will fit each girl and the issue of the heel height is another variable that may not make your identical bridesmaids look possible.
If the dress you’ve chosen is long chances are the shoes they wear won’t be seen so does it really matter what they wear on their feet? (As long as the style coordinates with the formality of their dress, of course. ie; no sneakers)
For shorter dresses, where shoes will be seen, you can ask your bridesmaids to wear the same color but let them choose a style that’s comfortable for them, especially regarding heel height. Remember, they’ll be walking, standing and dancing for hours so they should be in comfortable (and complimentary) shoes.
This is why dyeable shoes were invented.