What is voltage on VCC if board is powered on VIN with 7V?

As far as I can understand, VCC is equal to voltage of processor, so it must be 3.3V, even if I power the board to VIN with 7V.

Could you please confirm that I am correct?

Yes. 3.3V (example 8 MHz ProMini) or 5V (example Uno, Nano, or 16 MHx Promini).