My red cherry tomato plant’s leaves were purple when I went to check on them today, is there a natural explanation ? Also can I still eat the tomatoes off a purple leaf plant?(brief history – I use a community garden(pay for a plot), so I am not sure if another used chemicals on their area and transferred onto my plants or through the ground. I was there picking Saturday everything looked normal and Tuesday I come back, two/four plants are purple.)
The problem you are facing is a common one at this time of year. Plants exhibit purpling of leaves & leaf veins when there is a shortage of Phosphorus (P) in the soil. Tomatoes are heavy feeders and could use a boost of nutrients around about now, as they could have depleted what was initially available.
The best way of giving your plants the phosphorus it needs is some Bone Meal, sprinkle on and then lightly work into the soil. Do this carefully as you don’t want to damage any plant roots that may be close to the soil surface.
Another alternative is to use an all purpose fertilizer which would give it the other macronutrients (N & K) along with a variety of micronutrients.
I’m including a link below, on common tomato plant diseases, as a resource. Should your plants not return to green with feeding and it looks like you have bigger problems, you can use this as a guide to make a diagnosis and source a treatment.
I think the tomatoes from you plants are, more than likely, still fine to eat, but I would give them a good wash before consumption. If you have doubts about ingesting them, the decision is entirely yours.