Please can someone help clear something up for me?

I'm having problems with my steering in that it feels vague going round corners. There is no noise just that it seems to be understeering. I've had the ball joints checked and they are fine.

My mechanic looked at my power steering fluid and it is very dirty almost black so he suggested this was the first thing to change. However thats where we have come against the problem. You can see that the fluid used to be pink but when I look in my owners manual it says it should be M2C204-A which is a green fluid??

Obviously I cannot mix the two different fluids so to enable me to put the green fluid in will require a complete flush of the power steering system. But what I dont understand is that if the car has had pink fluid in which I think is incorrect why has it not felt strange from the first time I bought it in June 2009?

Should I just empty the reservoir and replace with pink fluid or should it have the green fluid in it?

Any help would be greatly appreciated! Thanks!