Oxalis?

This plant is growing in a large, cast iron cauldron outside. I bought them three years ago as a colourful balance to other things I planted in the cauldron. In the autumn the other plants died but this one was very alive so I let it stay over winter. It survived and grew bigger and bigger, now it's almost taken over all the space. I remember the plant I bought was a kind of red wine color with green in the middle but now half the plant is half green with red in the middle and even some with half one leaf red and the other half green. It's very pretty but I can't remember what it's called, maybe a kind of "Oxalis" plant?