>>17586Glad you find it useful. Here are a few other things I just thought of/realized…
White balanceYou've got to use photos with good white balance. A yellowish photo or one that's got some sort of weird filter on it will probably not work.
Record an action for the channel swappingLook up how to record an action for Photoshop. Create one for swapping the red and blue color channels, and map it to a function key. This will save a lot of time.
Mask behaviorI just realized that if you're using quick mask you can change the settings to make selecting an area easier.
>https://helpx.adobe.com/photoshop/using/create-temporary-quick-mask.html#change_quick_mask_optionsChange the color indication setting to Selected Areas so you don't have to inver the selection later.
You can also choose a dark blue for your indicator color and turn up the opacity so you can almost get a preview of how your selection looks.
Brush opacity/strengthIf you're using the brush and eraser to select areas of skin in quick mask, don't use a brush with 100% hardness or opacity. Dial down the hardness (I actually do 0%) and turn the opacity down to something like 30%. Make multiple passes, starting with the area you want to be darker and then spreading outward with ligher brushes. You can even make splotches in random places to make it look like the blueness is emerging all over at once.
About the pics attached here:
The 3-photo image shows the result of a selection; then the result of a whole-photo color change (which can be done easily in this case because background and her clothes are black & white); the last one is an experiment with using HDR to turn up the texture and details in her skin.
Also attached just the HDR one because I like the way it turned out.