Thanks, John&Joey.
The DICOR link says "if membrane has black backing, it's EPDM, and if it's solid color through than it's TPO". It is "solid" black color all the way through EXCEPT for white surface, which is painted.
So I phoned RV manufacturer, they have no clue other than material is "Dicor gray roof" (sort of gray-ish shade, to me it looks white).
Then called Dicor, they only could tell that if it is a Dicor material, than Dicor lap sealant will work no matter whether it's rubber or TPO. For competitor's roofs the choice of Dicor sealant does mater (i.e. Lap sealant or Ultra sealant), but for Dicor roofs they said it doesn't.
Oh well...