Cell's appearance didn't change with his version of the SSJ2 form (likely because he has no hair), so how would he look if he attained his version of SSJ3? Identical to his SPC form, just lighter colored?
Obviously he can't have hair and already has no eyebrows so the best thing to do from a design standpoint is to give him spikes like 3rd form Freeza to evoke SSJ3 vibes.
