Mine is doing the same thing. It's hot and rainy here. I would cut the tips off of each stem and fertilize. What is your zone?

In terra cotta on stones? I don't imagine that would be a mint's idea of a good time. Try a non-porous pot in a cooler location.

FataMorgana

It also looks like it may be too big for the pot after this time. Mint is a vigorous grower and you may need to prune the roots.

I've had a problem with my Arabian mint doing this. It's in a small pot and when I forget to water it it looks like that. Mints like water, usually. I just pee on it and it starts to green up right away. Just make sure to dilute it a bit. May want to pot it up in a larger pot and add some nice dark soil if you have it. I wouldn't stress it out any more by pruning or cutting anything yet. It looks like it may have a nitrogen deficiency too due to the lower leaves yellowing. Make sure to water it, they hate being dried out, and in a terra cotta plant those things dry plants out pretty fast in the hot sun. And too much sun (if you're in a blazing hot place) they don't really like that.

I agree with ninkasi. The plant looks as if it has filled the pot and could do with repotting.