undertone

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An underlying or implied tendency or meaning; an undercurrent.
• noun A tone of low pitch or volume, especially of spoken sound.
• noun A pale or subdued color.
• noun A color applied under or seen through another color.

from The Century Dictionary.

• noun A low or subdued tone; a tone less forcible than is usual, as in speaking: as, to say something in an undertone.
• noun A state or degree of tone, as of the physical or mental faculties, below their usual condition. The color of a pigment when seen in very thin layers on a white or light-colored surface.
• noun In musical acoustics: Same as combinational tone (which see, under tone), One of a series of tones reckoned downward from a given tone in exactly the same way that the series of overtones or harmonics is reckoned upward. The interval from the given tone to the first undertone is an octave; to the second, an octave and a fifth;

from the GNU version of the Collaborative International Dictionary of English.

• noun A low or subdued tone or utterance; a tone less loud than usual.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun an auditory tone of low pitch or volume
• noun an implied meaning; an undercurrent
• noun a pale colour, or one seen underneath another colour

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a quiet or hushed tone of voice
• noun a pale or subdued color
• noun a subdued emotional quality underlying an utterance; implicit meaning