Expanding on this answer:
If you have Adobe Illustrator handy:
Window > Image Trace > Advanced
The result in my image was very identical, only thing I noticed was that the result's borders grew by 1 pixel, not noticeable at all, you will only see it if you zoom maximum (12800%).
I know that OP asked for Adobe PS, but since SE is a knowledge website and ...
I was working on a file with a transparency problem. The transparency panel showed 100%. First I opened the Appearance panel, and selected the Hamburger menu and then selected Clear Appearance. When I went back to the Transparency panel it showed the image at 50% and I was able to change the transparency.
Possible solution for Gimp 2.10:
Put your image in a group
Add a layer above it, set layer mode to Color erase (this mode is new in 2.10)
Paint the layer with the color you want to make transparent
Use additional layers for additional colors (you could use several shades of green...)
You can put a layer outside and below the group to check transparency over ...
You can try GIMP's Color > Color to alpha. You must combine with layer masks
one version which is otherwise well separated from the background but the wings are still green
another version where the wings are transparent as wanted but something else green has also vanished
Hopefully you have a high resolution photo. The shown version in the question is ...
If you can paint on opaque areas but not on transparent areas, make sure that the layer is not "alpha-locked". The alpha lock is the checkerboard icon in the Lock: line at the top of the Layers list. When it is set (this is sometimes hard to see), you cannot change the opacity of the pixels, so you cannot paint on transparent pixels.
If you cannot paint on ...