Here's a link to a chart on tomatoes. I know that seems strange but I doubt if your plant is much different. In the past, people have said that purple on a plant is a result of phosphorus deficiency. If you scroll down this webpage to the chart where it says "Table 1," the first thing listed is "purple leaves." It says a lack of phosphorus is the cause. Your fert is a little short on this nute so you might consider increasing the dose or switching ferts. You'd think the product would be good for the plant, with the money you spend on it, but perhaps you have a strain that need more phosphorus or there's a problem going on that prevents the nute from being used. It's hard to tell. I'm guessing this is the problem, but I'm not an expert. Just found this on the web regarding your problem.
Recognizing Tomato Problems