Selecting portion of an image

I have posted a picture that I would like to be able to select a portion of the image to change its color. I have tried to crop the image and put each part on a button but with the curves, it is hard to select the entire portion of the color without getting into the next color a little bit. I have visited this probably simple procedure many times over the last few years but have quickly lost interest because I just have not been able to figure it out.

For instance, I would like to be able...

Selecting portion of an image

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