Colored box behind a single note

[Werner LEMBERG]

Using

  http://lsr.di.unimi.it/LSR/Item?id=1000

I wonder how to get the effect for a single note.  Ideally, I would
like to write

  \genericSpan <...parameters ...>
  e\startGroup\endGroup

but since `\genericSpan' uses a `HorizontalBracket' grob, this fails;
it needs at least two notes.

I wasn't able to find a suitable solution in the web; IMHO, it would
be a quite useful addition to this snippet.


    Werner