The name of a pale blue angling fly?

"W. D. Grey" wrote

As Mike says, in the UK this is an old Northern standard pattern serving
as a representation of the Iron Blue dun. A hackled fly always fished wet.

the Dark Watchet is alsoe know by other names viz.

Iron Blue Dun
Little Iron Blue
Little Water-hen (when wings are needed the breast feather of the water
hen are used)
Little dark Dun

and, as any welshman worth his salt would know, is called, formally,
*paraleptophlebia adoptiva*.

yfitons
wayno(surprisingly, they are seen in numbers on big snowbird in late march,
early april.)