I personally think this always gets blown out of proportion. As someone else said, if you're good enough, skin colour makes no difference.
It is also a fact that there fewer black people in this country than white and also fewer black players, so it stands to reason that the majority of managers are going to be white.
We've had Gullit, Hughton and Ince as managers, and a lot of black ex-players have turned to punditry.
I don't think there's any agenda, it's just the way things have happened.