My tomato leaves turned purple?

Well, how strange. Ours have been fine, but it's something to look out for. I must tell my DH about it when he comes back from Scotland.

Dunno what you could do about it, though!

I was always lead to believe it was the cold that turned them purple but hardly applies to during the summer

I think it is cold and/or a shortage of potash, either because the compost is deficient in it or because they can't take it up so well when they are cold - but it might have been phosphorus.

I had purple tomatoes, but they were suppose to be that colour!

Mine didn't recover with phosphorus......

I had supposed-to-be purple ones too but they were brown, and I don't know if they were right or not!

Cold can do it. It's not a mildew is it? my garden has had a lot of that This year. The clematis were wilting right left and centre. Me included

Alie my 'Black Russian' tomatoes were a weird shade of brown but delicious to eat.

Not mildew, no.
My brown tomatoes came from China!
My best ones, though, came from a cross the year before, Sweet Million (tiny salad toms) X big beef toms (forgotten what kind).....large and sweet as well. I kept seed to see what happened.

I can only think of lack of magnesium.

They were given magnesium, potassium, phosphorus and every kind of tonic I could find - in succession. not all at once......

The leaves at the top of each plant turned purple and practically stopped growing. The tomatoes lower down ripened normally. Very odd.