It's called and escutcheon, usually.

Are you looking for the ceramic white cap that has a hot or cold written on it that goes in the center of the handle ?

thanks palimpsest

lillo, yes i'm looking for ceramic white cap. I don't need hot/cold written. Plan white is good enough

The escutcheon is the white thing to the right, those are handle buttons or caps

Here is a link that might be useful: DEA bath

The link supplied above has them . I have the axor Montreux hansgrohe set , it has the white ceramic cap . You can find them in the accessories of that set .

Thank you both :)