Do any of your other plants have the discoloration on the leaves? Do you mean gray mold? It looks like spider mite damage to me. But the time, temp etc aren't really rite. If it were me I'd isolate it from the other plants, just as a precaution.
That is a great site, I just know of a couple diseases that start out looking similar to that. It may just be the crazy weather but I recommend keeping an eye on it and if it gets worse don't ignore it. Are they in the ground? I usually see a slight purplish discoloration before the disease spreads on the plant and to other plants. Keep us posted, please. Always so much to learn.
All of the first ten tomatoes I set out looked just like the one you are showing. They were just smaller than yours. I think it is the cold spring and we had to leave them in the cold frame to long. As the temperture warmed and they began to get their roots down and grow, I put just enough Miracle Grow in a bucket of water to turn it a very pale blue and poured about six ounces arount them. They have turned a beautiful dark geen now and have jumped to about a foot high.