Tomato Plant Turning Black?

I potted a tomato plant in a white bucket and filled it with soil a little over half full and put it on the porch as we live on the second floor on a busy street. I noticed the plant itself was turning a dark color. I gave it some Miracle Gro and the bottom leaves on the plant went yellow so I took those off. Now the rest of the plant has turned just about all black. There are 2 tomato's growing at the top and they are getting big. What is the plant lacking?

By Gail B