I have black ugg boots that have faded to a gray colour can i dye them black again?

No, it is probably too late. You should have taken better care of them when they were new by using the ugg care kit: a href="http://bit.ly/aeBJ4d" rel="nofollow"http://bit.ly/aeBJ4d/a If you do not take proper care of your boots, the color will fade, unfortunately