ardenrj - there is some reasearch on exactly this subject here on the forum...do a search for "white roof" or "White panel". I can't find the thread but a few members actually setup a sample test using different paints and measure the temps.
As for what it is...likely to be white Kool Seal. It's available from almost any RV dealer and from Camping World. There is a special version for metal roofs and a primer as well.
Also, most new AS have the top panel painted white. I know this is the plan for mine....less area to polish!
1986 Airstream 345 Classic Motorhome