That doesn't make any sense to me... the darker the colour the less dirt will show, I thought that was basically for everything.
BTW, I hate the silver grey colour as well.
It most probably doesn't make any sense because you've never had a black car. A couple of my friends traded in their black cars because they just couldn't stand them looking so ugly - one was a Beamer SUV and the other was a Beamer Saloon.
Silve grey is the pits, but it looks "good" longer ....