Well, the large size didn't work... so I tried playing around with the small one.
First: Too dark, so I fiddled around in the curves. Brought up the midtones, downed the shadows and raised the highlights a little to give the mushroom cap more brightness while keeping the rest a little darker and deeper.
Second: I pulled down the blue curve in the midtones, I guess, and that warmed up the color very nicely, and made the cap a nice yellow gold.
Third: It's awfully noisy, isn't it? I decided to try GIMP's Despeckle. I set it on recursive, radius 3, black level 7. I don't really know how Despeckle works. I assumed it was noise reduction, and it is. But it's extremely powerful, or maybe it's meant to be used on really really huge pictures. When you use it on a small one.... this happens:
