Against other platinum, exactly, and permanently - platinum has no plating, so its colour does not drift with age or wear.
Against rhodium-plated white gold the match depends on how recently that piece was plated and how much it has been worn. Plating applied at different times reads slightly differently, which is why a newer white gold piece can sit a little off against an older one.
If you are building a set over several years, platinum is the metal that stays consistent without any intervention.