What is the meaning of Undertone?

An auditory tone of low pitch or volume.

An implicit message perceived subtly alongside, but not detracting noticeably from, the explicit message conveyed in or by a book, film, speech or similar (contrast with overtone); an undercurrent.

A pale colour, or one seen underneath another colour.

A low state of the physical faculties.

To accompany as an undertone.

To say or speak in an undertone.

To present as less important, noticeable or prominent.

Source: wiktionary.org