Keep it up Christina - I recently noticed that threads can be rated. Yours are often very interesting ................
One thing I will say is that I suspect you made an excellent choice of focal length for the shot I played with.
On this one the trees are showing an definite cast that may or may not be present in the entire image. I'd guess looking at the rgb histograms that the blue channel is out of sink but have no idea how that would be shifted with the software you use. It might be that it's an aRGB colour that doesn't come out right on sRGB. Anyway I played with the mid point and highlight end of levels blue channel and this is what happened
Still not right but notice that a lot of the image has popped some what. I suspect what you need to do is to use levels and get the gamma, black and white points right initially before doing anything else. Then the selective work where needed
I'd guess that Adobe auto levels may well do the same thing as GIMPS does - alter setting in all channels. Try it and see what it does and get a feel for using them to even out the colour balance. This might help - he talks a lot but gets it across.
RAW --> CROP --> LEVELS ---------->
Whoops a link might help
https://www.youtube.com/watch?v=zTIBx_JZ3po
The GIMP but levels are pretty much levels. I'd be cautious about using up all of the output space as that leaves a problem if you want to do more to highlights and lowlights Like most things shots vary but this isn't a bad place to start. Something to look at before anything else.
John
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