This insect had a dark (appeared black) thorax with one central pale stripe, perched with wings spread (as here) on flowers, and the abdomen appeared "flat", not cylindrical. (Oops--should've mentioned that was also true for the other tiny fly, the one with black and white abdomen.) The thorax had a tiny iridescence but not enough to notice from a distance.

All four flies were on the same flowering elbowbush at the same time; there were other flies which I was not able to photograph. In this location, elbowbush is the first woody plant to flower (and one of the few plants of any kind in flower) and they do not all open at once...this was the very first on our place.