Oil color, any idea what this could be?

Ever see this color? Bought a BMW from auction and was fine. Driver test drove it and said all was good. He kept it in his yard until the week after until i bought more cars, so he won't have to make a drive for just one car. Next week he went to pick up other cars i bought. Dropped the x5 down to load others and he said it started knocking. Just strange. I dropped the oil, and it looks greenish. Not water, just weird looking. Never seen that type of color before.