The center diamond is a pinkish/prown diamond. Mine cut, surrounded by 4 pinkish brown mine cut diamonds, and 2 replacements (original stones fell out, haven't gotten to getting matching replacements).
I think you should try to match the replacements if you possibly can. If you can't, maybe you should have the white stones placed at the top and bottom, so the ring looks symmetrical.
You are very fortunate in the inheritence of your Grandmother's ring--it is very beautiful indeed. I peruse antique sites for a glimpse of these beauties!!!!!