I am travelling from India to Netherlands, and have Schengen visa for Netherlands. I have a flight layover at Frankfurt, Germany.
Do I need a transit visa for changing flights (same terminal)?
No you don't.
Once you enter Germany, you'll already be inside the Schengen zone. In effect, your flight from Germany to Netherlands is a "domestic" flight, because you don't need separate visa to transit between these two Shengen member states.
The single entry means you can enter once to the Schengen zone; so you'll be fine (as long as you don't exit the Schengen area - which as per your question you are not planning to).