I have pesonaly seen a very light colored one and I have seen a rug from one that was almost black so there are color phases,just not as common as a bear as far as I know.

I have seen a cougar that was totally black. I was out deer hunting west of Spokane,Wa when i seen it slinking along the botton of a canyon. I watched it very closely for a good hour and half in disbelife. I watched through my Bino's and then rubbed my eyes thinking I had seen some starving black bear with a long tail. When I told dad he said he had seen something of the nature also on a brush pile a couple years back but wasn't sure if he was seeing things due to an allnighter the day before.