I recently bought a 2006 Saab 93 Aero. The other day I got a warning message that I had low coolant. I bought Prestone Dexcool coolant which is completely orange in color but, when I looked in the coolant tank I can see the coolant was greenish. I took some out to investigate and when taken out it has a transparent orange color but as soon as I pour some on black plastic it turns to a less transparent neon green. (reservoir tank is black plastic) The Preston coolant stays orange on every surface. Is it normal for the coolant to change colors like this? Is it possible that the previous owner mixed orange with green coolant? Can I mix the old coolant with the new one I just got? Or should I flush the whole system?