Luiz,
These must be are amongst the best references on skin retouching and uses just RGB*. Let me correct that. The first one I have studied up to the procedure of making curves in a mask. The effort here is directed against unsightly areas such as as a babies rash or unsightly shadows. This is a curves layer with a gradient of numerical values. The actual values of RGB come (at one end of a gradient), from the wanted hue and tone, and, (at the other end of the gradient), blemish areas . Sounds complex, but do it once and then it will seem obvious. This is just at the beginning of the second page of the first of 3 tutorials by Crawford Hart. For this work, investment in a Wacom pressure sensitive tablet is a must! If one masters these early ideas, one hardly needs to go further! If you actually have the motivation to become proficient and practice enough, this will be another way of sucking up your time but the results will be flattering to your subjects.
Everything in layers!
Asher
*Crawford Hart also gives a reference to LAB methods, but key images are missing at that thread.