Just For Men is called so, because a lot of men would feel embarassed going into a shop to buy a 'womens' hair colour. They basically have the same ingredients as 'womens' hair colour, but with different packaging.
Hmm, not sure why, butwhen i was at hairdressing college several years ago, we were told that womens should noyt use either just for men or Grecian 2000. I can't remember what the reason for this was now...