I didn't unfortunately get a picture of this one with it's wings open, but the topside was a lovely dusky blue and brown. I added a enlargement of it's waggly rear end which looked like antennae which I suspect was to confuse predators.
I thought this one might be a Stencilled Hairstreak, particularly also given your description of the upperside. But I'm convinced your other posting this day is the Imperial Hairstreak. Suzi will adjudicate, of course!