I wonder if your plant needs more nutrients? Could that cause the color to look different?
The only thing I know about the triangle leaf Oxalis is what I learned from my dog recently.
He likes to dig (yep, I say that quite often, sorry
) and he absolutely destroyed my cute little Oxalis plant when he was helping me dig and I was not paying attention.
Two - three weeks later...over 25 new Oxalis plants have started growing in the area where he had been digging. Guess you cannot kill these plants! I dug each one and potted them up, keeping them in the shade to share at my local swap.