You asked about extra keys on a big grand.  I believe Boesendorfer
is the only one that does this.  My mother used to sell Boesendorfers.
The story, as I understand it second-hand, goes something like this.

Someone wrote piano music that required more keys than a standard 88-
note piano.  Boesendorfer custom-manufactured a piano with extra keys
just for this application.   In order to accommodate the extra keys,
the sounding board had to be made larger.  The larger sounding board
sounded so much better that Boesendorfer decided to manufacture all of
their larger grands with the extra keys and larger sounding board.

I have seen some with the blacks and whites reversed as you observed.
I have seen others with a hinged block at the end of the keys that
folded over the extra keys.  With the block down, it looks fairly
conventional.  The block is folded up to access the extra keys.

Gary Rasmussen
5520 Homecrest Lane, Mason, Ohio   45040  (Cincinnati Area)
phone & fax (513) 336-6209

 [ I've seen two Boesendorfer concert grand styles: the smaller
 [ with 92 keys, and the Imperial Concert Grand with 97 keys extending
 [ the bass all way to lowwww "C" !  I'm told that the extra keys are
 [ in inverse color to alert the pianist, but I suspect it's mere
 [ "styling" to grab your attention when the piano appears on TV.
 [ The black hinged cover over the extra keys helps to make the keybed
 [ appear more normal (provided especially for anxious pianists!).
 [ I think Debussy and Ravel wrote pieces with extra, optional low-
 [ bass notes for added sonority.   -- Robbie