What would make platinum yellow?

[Logan Sapphire]

My husband dropped my platinum (950) ering off to be re-appraised and the woman who helped him thought it was white gold b/c the shank was yellowed. I know for a fact that it truly is platinum (the stamp was erased in order to engrave the inside) and it's been appraised/acid tested as platinum.

What could cause a platinum ring to be yellowish? It's never been sized.