What is the pigment chemistry behind older permanent makeup turning red or gray over time?

Permanent makeup dyes are generally obtained by mixing red, yellow, black, and white pigments. A brown eyebrow dye contains all of these colors. If the dye used is of poor quality, or if the wrong pigment is chosen without considering the person’s undertone (warm/cold), color change is inevitable. Black pigment molecules (carbon black) are very small and are the last to be broken down by the body; when the yellow and red colors fade prematurely, the eyebrows will gradually turn a gray-blue color. If the iron oxide in the dye is of poor quality and the black color fades prematurely, leaving behind a dominant iron oxide red, the eyebrows will gradually turn reddish or orange.