Can zirconium crowns get stained? Mine already have gray stains on them. (Photos)

I put about 20 zirconium crowns a few weeks ago (in another country), and they already have gray stains on them. The last two are implants with crowns, which has a dark bottom part (see pics). Not happy esthetically either. I'm a coffee drinker but I didn't think that they would stain. I brush with an electric toothbrush and use water pik daily. Are they zirconium at all? What could have caused the stains? Please let me know what you think of it and what should I do about it. Thank you.