Photo retouching is a complex art and it comes with countless options and possibilities. In fact, the only limitation is your skills and imagination. Color grading is one of the last steps in my editing workflow in photoshop. It is best to leave coloring and toning until the image is fully edited. Any changes to contrast, sharpness, vignetting, etc. will amplify or reduce colors and saturation. Those always effect toning and mood of the photo so again it is best to wait till you are sure that the image is finalized.
Having said that, very often it happens so that I revise my editing either after I finish working on it, or the next day. While retouching a photo I change the zoom very often, so I switch between details and global scale all the time. It is possible to miss certain things when I am redirect a narrow focus to a problem area. It is essential to review your work after you are happy with the final result. If you are a obsessed with details like I am, you will always find something to be fine tuned.
The way you color grade your image will depend on the model, mood, lighting, retouching style, your photoshop knowledge, artistic concept and vision the photo was taken with, and so on. There is no recipe for photo toning and no preset that should be applied. Every single time you will encounter different colors on your images, so the color values that you will apply during toning should match those. Applying presets and photoshop actions is a lazy way out and produces rather poor results. Take your time, look at the building blocks of the image and try to sense what type of toning would fit this particular photo. It is your art and your decision, do not let presets created by others mindlessly decide for you.
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