there are several brands out there but all for "gray" are intended to get rid of the yellowing that white hair gets from air pollution, shampoo build-up, etc. I use mine (have allowed white to show since age 31--30+yrs later it's almost all white)about every other week. Every brand I've used is a dark purple, you leave suds in for about 5 minutes and then rinse--don't worry, these are made not to leave you a purple haired old lady.