I've recently acquired a small spearmint plant, that I still have in its original pot, since I haven't had time to pot it yet in something larger/more normal.

The spearmint was nice and green when I first got it. I've not watered it since there has been occasional rain.

The leaves are now turning purple/burgundy and I have no idea of why this is happening.

It's still in its original soil mix from the little garden shop I got it from.

I've not watered it much and have had it out in the sun which hasn't been as consistent these days since there has been some cloud clover.

Can someone PLEASE tell me why this is happening to my plant? Am I doing something wrong? Is this going to ruin the plant? Is it dying?

Are those leaves still usable?

How do I get it back to green? Will it ever turn green again or will they stay burgundy and die?

I've attached a pic below. I'd appreciate any help you guys can offer, I'm so worried.

Thank you.