See attached images. The old face inherited from `font-lock-type-face',
and the appearace was OK (though not wonderful).
 
The new face inherits from a face called `success'. It is uhhhhgggly.
 
For one thing, it should not be bold.  We should almost never use a bold
face as the default face for something, because boldness does not work
well on some platforms and for some (many) faces.
 
I applaud not inheriting from a font-lock face: there is no logical
connection to a grepped file.  But there is also no logical connection
to "success" here.
 
Anyway, whatever you inherit from (but why must you always inherit?),
the default appearance should not be ugly and difficult to read.  That
just forces more users to customize it or live with the difficulty.

In GNU Emacs 24.0.50.1 (i386-mingw-nt5.1.2600)
 of 2011-08-22 on 3249CTO
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (4.5) --no-opt'