sealing dark granite in kitchen

Maurizio,
I went to your site for advice and found it extremely informative!  Our
counters are about 6 years old and still look nice.  My wife and I
disagree on whether or not to seal.  She's heard that the seal might
yellow over time and you can't remove it.  She's especially concerned
because the kitchen has lots of skylights and high windows, so the sun
beats on the counters intensely.  I think it s/b sealed for protection,
especially around the sink.  I believe the common name for our granite
is Dakota Mahogany.  It's dark - overall lots of brown, reddish-brown,
gray, and black so it doesn't stain easily.  What do you recommend?
thank you, Craig