Caught this dragonfly on camera as it visited my flat this morning. I'm in London by the River Lea, very near Leyton Marshes.
The wings in sunlight almost glistened like gold! Picture is taken as it sunned itself and so the head and strip colour is hidden a bit by the glare, but it was a pale green. I'd estimate that it's about 7cm long from head to the bottom of the of its body.
This is difficult for the reasons you know about (lighting obscures the colours). However, we can see orange/brown wings and the thorax looks brown with two pale stripes. The body looks to me to be brown and on the last big segment before the narrow bit (S2) there seems to be a small blue spot on the top while on the first narrow segment (S3) a large blue spot underneath.
This seems to suggest a brown hawker (Aeshna grandis)