Don`t worry about it, It`s normal. I think it has something to do with the seals discolouringthe fluid when the clutch is operated. A reaction between the fluid and the seals. There are threads on AF1 about all this.
Mine's as black as the ace of spades, with no discernible effect. What's that I hear you say? "Slack *******. Should maintain his Italian Stallion better than that! It's a job for Ron, I reply - later Ron::kicknuts