Purple leaves

[ZachLosko]

So a random thought I had the other day. Why is antho/purple leaves somewhat common on pepper plants. But, I don't even think I have ever seen a tomato plant with purple leaves (that was not just nutrient deficient)? Which just seems strange to me since tomatoes and peppers are both in the nightshade family. If anyone has any reason of why this is, I would love to learn!