1)Student's Guide to Painting by Jack Faragasso- currently of print, but I was told by Mr. Faragasso that may change in the near future
2)Values for Pictures Worth a Thousand Words by Apollo Dorian- Also technically out of print, but you can send away for it.
3)Mastering the Craft of Painting by Angelo John Grado- Also out of print but affordable
In short the "Reilly Method" utilizes a form of controlled palette in which you mix up to 10 values of reds, yellows, grays, fleshtones, and sometimes blue. I generally limit it to 5 to simplify for my student.
In Reilly's teachings he would preach a way of calculating value accuracy through a combination of local value and a given planes angle to the light source. This requires a long term dedication to the study of form and its ability to refract light. To simplify I tell my students that on the average person the general value of flesh in the light is a 2 (if numbering 1-5, left to right on the chart above) halftone (planes at an oblique angle to the light) are a 3, general shadow(planes facing away from the light source are a 4, dark accents a 5, and highlights a 1. This of course is a huge over simplification, but a good way of learning to control your values when beginning to paint in color. You can increase accuracy and precision by adding more values, but this will also add complexity.
Once you have established the correct value (often done using a burnt umber pick-out form of grisaille or underpainting) you can adjust the generic flesh tone by mixing in the corresponding red, yellow, or gray.