fair timber
I’m really not liking how dull this wing looks.
I think the first third of the wing (starting from left) looks alright, but the rest looks really dull. I’m trying to follow the picture I took of it when I painted it black and shined a light on it, but I think I picked the most boring angle. Should I keep going or try another angle?
fathom sparrow
My recommendation would be to push your shadows. Right now it's a blob of highlighted green with a touch of yellow. Add some interest into the darker regions by colour spreading towards the next colour on the colour wheel - in this case you're using green so highlight towards yellow and shade towards blue.
Simplest method - glaze in some blue washes into the recessses and feather them out with water to weaken the effect the further out from the crevices you're going