If you load a streetview you might see a split second of color, before the (flash) sepia filter gets added.

If you turn on 3D mode (right mouse -> 3D mode on) the ring and dust/scratches remain, but the sepia filter is removed.

If the maptype parameter is 8 (&t=8) assets get loaded from the "papermaps" directory:

  https://maps.gstatic.com/intl/en_ALL/mapfiles/papermaps/

Instead of:

  https://maps.gstatic.com/intl/en_ALL/mapfiles/

This way I found an image of the map controls that isn't implemented:

  https://maps.gstatic.com/intl/en_ALL/mapfiles/papermaps/mapcontrols3d2.png

Notice the squiggly lines and the streetview icon.

The world map seems to be indeed just images. Compare:

  http://maps.gstatic.com/mapfiles/mv/hpimgs6.png
  http://maps.gstatic.com/mapfiles/papermaps/hpimgs.png