They're orange-red, about the size of an adult aphid, and suck the juice out of the leaves from the bottom, leaving ugly black spots all over. They're quick to jump off the plant when disturbed so I can never seem to get a good look at them, catch them or even spray them.
I actually just remove all affected leaves, shoots, and sometimes entire plants. I own up to planting my mints directly in the ground
. I don't care what they say, it's much easier to rip entire sections out and dispose of them when you have plenty of mint growing elsewhere. 
You just have to stay on top of it, but mowing and walking on them also keeps them within bounds. 
Every year, I pull out mounds of mint by the roots, pot up some to give away, and toss the rest on top of the English Ivy infesting the woods behind my back fence in the hopes that the mints would root and give them some competition. So far, it hasn't worked, but I don't actually *plant* them among the ivy either.
As for the much maligned Ground Ivy (in the mint family) -- the few honeybees and bumble bees that I have seen this spring were always visiting the Ground Ivy flowers. Just this morning, I saw a bumble bee with pollen baskets.
) They are doing fabulous so I will have to keep an eye on them for these pest.
and it has a MUCH worse infestation there. They're even getting into the Ground Ivy. 