I think it's a common occurrence with this grass. The contrast is awfully nice to my eye.
You can't leave it there forever as the phytosynthetic virility of the all-green parts of the clump will eventually take over. But you could certainly enjoy the combination for a season or two or just immediately dig those parts up. Give them away to a gardening friend or start a drift elsewhere in your yard.
At any rate - enjoy!
James.