You can replace the caps from any MX switch regardless of color. In fact, MY (G81) keys will work as well. One thing you may have to keep in mind is that cap mounting from some manufacturers may be different than others. Cherry keys work on Filcos for the most part except on some of the larger caps where Cherry likes to mount the cap off-center and the Filco is center-mounted (Space and Caps Lock come to mind). Board-to-board, caps that fit the same switch family will work for single-sized caps (letter, numbers, etc.). The only other thing to be aware of is cap height. Filco caps are taller than Cherrys, for example. It doesn't affect key travel, or anything, but it might look a little weird if you mix caps from different 'boards.
Sorry for the rambling post. It's still early, and I haven't had enough stimulants yet.