I don't know if this will be of interest; most people probably already know this. There are many ways to determine your skin undertone. The easiest way is to look at the color of the veins on your wrists. If they're blue, you definitely have a cool undertone. If they're green or purple, you have a warm undertone. If the color is indeterminate, or if the veins on your wrists are one color and on your creases another, you have a neutral undertone. I hope this will be interesting to some. Gold or silver, or reference colors, are also used, but that's the easiest way.