Oil painting question?

I received a large canvas to do a painting on. The canvas however had been damaged, not really damaged but stained. Apparently a raccoon had taken a dump on it. I knocked off the feces as best I could and used bleach at first, but then my art teacher told me that was too harsh of a chemical to use. So later on I took sponges and mixed water with detergent and cleaned the whole canvas down very well. I let it dry and then I decided to stain it with a burgundy color oil paint, so that I wouldn't be working on a blank white canvas. I mixed up the paint, very thin. I put it on the canvas and it dried quick. But in the places where the turd stain was, the paint turned black. On the front it seems grey, but if you look around back its like a deep black. I don't know what caused this. How can I fix it?