Platinum comes in all shades depending on what ratio it's mixed with other elements. I don't think anything short of a spectral analyzer (or whatever that machine they use at high end jewlery stores is called) can determine something's true composition. A simple photographic analysis through an app is probably grossly inaccurate, especially considering that aluminum, steal, iron, lead, etc. can all appear with a similar visual appearance to precious metals. I remember finding alot of bootleg jewlery that looked so real but turned out just to be superficially similar due to the bootlegger using a good base metal alloy for the deception.
In short - get your samples analyzed by a professional. 😄👍