I took this video (by digiscoping) a Maxey pits this morning, in order to capture the upperwing of a female Clouded Yellow that lacked yellow ochre in the forewing (I could see it in flight, but it is very difficult to photograph.
In the video, you can see the butterfly feeding alongside a hoverfly until another comes along and sees it off, allowing a flash of upperwing (before a flash of my jeans...).
I took these screen grabs to show the upperwing pattern. Pale Clouded Yellow and Berger's Clouded Yellow females lack the extensive black around the upper hindwing and also the dusky grey cast to that wing. I think this confirms it as a female of the form helice.