Well... while there's no such thing as "the grey side of the Force", Revan would be considered a Grey Jedi when he went against the Order's wishes and joined the war effort against the Mandalorians.
I know this is completely besides the point you're trying to make, but still. :P
Well it depends upon your definition of grey, the proper grey balances light and dark, but Revan at that point was transitioning between the two sides (not that this was his intention), which is not the same. But you could make an argument for either viewpoint.