I think in mine when the head goes all white they are really excited or really mad. I never trust them when the head is white.
I had one with a white head walking towards and alongside of me tonight and giving me stink eye.. I explained to him what happens to a Tom that should do something stupid this close to Easter.
Mr. Ts head has only gone white once. And that is when a child was harassing his hen. That was last spring. Other than that he has never "gone white" on me.