Hi Pammie, that sounds like frost damage sadly. you may find that any white parts are still edible. I am surprised they didn't go onto flower in the autumn.

Maybe too late now, but bending the leaves over the "flowers" prevents both sun & frost from discolouring the head

I'd leave them alone if space allows, as SBG says they may be OK underneath, and come spring could be a source of fresh "Greens"

Thanks for helping me with your Comments x