I think the best you could hope for is to mute the grey a little. Turning it white-ish would be near impossible without either affecting the transmissibility of the foam or, worse yet, the solvent in the paint will dissolve it. I would think water base would be your only choice.
Were it me, I'd learn to live with it. The drivers are black, which creates a pretty high contrast...no?
I'd sure experiment on some scraps before I went after the cut pieces. Maybe some fabric spot glued, but my mind's eye says no. Yours may say something else.