What kind of oil are you using? German made Castrol Syntec is green. The only way to know if it is German Castrol is to look on the bottle to see where it is made. Actually, I guess the other way is to notice that it is green when you pour it in.
At this point you don't have enough to go on. In my experience when coolant gets into the oil, there isn't any trace of green in the oil.
