Old things CAN be new again, sometimes. I took this old painting that had been hanging around since about 2007 and threw some new paint at it. As long as I stayed in the correct value range (light to dark), I could add any colors that I wanted into all areas of the painting. Here is a closeup of the area on her cheek and neck:
I was able to add notes of purple, green, blue, and orange into this area of the model. Since each of these colors was the correct value, none of them stood out and away from the others. Sticking with the correct value actually frees us to experiment with color!