Hi Peter (assuming this is your photo, not Sally's) - this is probably a male half way through developing its blue pruinescence; the thorax is still yellowish, and there is a bit of yellow still on the distal abdominal segments. Unfortunately, the anal appendages and the ventral profile of the second abdominal segment, which would clinch whether this is a male or not, are not clear in these photos. But the possibility of this being a female with well-developed blue pruinescence is interesting.