Using the same technique, copy the non-reddened skin to a new layer. In
the next step, you’ll have to differentiate between the source layer and the
layer to edit, so rename these two layers meaningfully; all it takes is a
double-click on the layer name. You could use the naming scheme shown
here and call them “Beautiful skin” and “Reddened skin.”
Activate the layer with the red skin, and select Image → Adjustments →
Match Color from the menu. For “Source,” select the current document, and
for “Layer,” select the one with the beautiful skin. Control the effect using
the “Luminance” and “Color Intensity” sliders in the Image Options area.
Once you confirm, you can control the effect’s strength with the Opacity
slider.