1762, "low or subdued tone," from under + tone (n.). Figurative sense of "undercurrent of feelings, etc.," is attested from 1861.

a quiet or hushed tone of voice; "spoke in undertones" a subdued emotional quality underlying an utterance; implicit meaning a pale or subdued color (The Undertones) The Unde [..]

(n) a quiet or hushed tone of voice(n) a subdued emotional quality underlying an utterance; implicit meaning(n) a pale or subdued color

A subdued color; a color that modifies another color. The color of paint viewed through transmitted (reflected) light. It may be caused by using a top coat that's too thin or that's lacking [..]

In cosmetics, undertone refers to cool or warm tones of the skin. Your undertone is determined by the color of your eyes, your natural hair color, and which colors make you look pretty. Most foundations are based around the undertone of the skin.

Undertone is a term used to refer to the tone of the skin, like warm or cool.

a certain colour of pigment used as a thin and transparent layer.