undertone

Etymology

under- + tone

noun

1. An auditory tone of low pitch or volume.
2. An implicit message perceived subtly alongside, but not detracting noticeably from, the explicit message conveyed in or by a book, film, verbal dialogue or similar (contrast with overtone); an undercurrent.
3. A pale colour, or one seen underneath another colour.
4. A low state of the physical faculties.
   Sedentary occupations are likely to result in undertone, and this undertone not being relieved by physiological means, constipation is a probable outcome. 1905, Medical Review, volumes 51-52, page 171

verb

1. To accompany as an undertone.
   The Missionary's address rolled on in choppy Chinook, undertoned by a gentle voice from the back of the room which told Tanook in pure Indian words what he was to do. 1941, Emily Carr, chapter 1, in Klee Wyck
   Undertoning the howling siren I was aware of a distant swish, like that of a hurricane’s forerunning wind through palm fronds. 1951 January, Arthur Leo Zagat, chapter 7, in Fantastic Novels Magazine
2. To say or speak in an undertone.
   Evan paid no attention to him, and answered none of his hasty undertoned questions. 1861, George Meredith, Evan Harrington, Chapter 30, Part 1
   At first, when the net was being prepared, those children of the forest had merely stood by and looked on with curiosity. When Blondin and his men rowed out from the shore, letting the net drop off the stern of our boat as they went, they indulged in a few guesses and undertoned remarks. 1887, R. M. Ballantyne, chapter 13, in The Big Otter
   “He handles that pallet like it was a mule,” McCoy undertoned, passing Mason. Mason grinned and fell in behind. 1984, Greg Bear, chapter 11, in Corona, Simon and Schuster, published 2000
   “How come there’s never any birds in cemeteries?” Skelote undertoned. “Squirrels, rabbits, but no birds.” 1999, Thomas Sullivan, chapter 35, in The Martyring, Crossroad Press, published 2015
3. To present as less important, noticeable or prominent.
   Men rarely make this mistake, their habitual blunder being to undertone everything, to make too light of Julia's new frock, and Johnnie's symptoms of measles, and the way they waste things down stairs. 1866, {unattributed}, Littell's Living Age - Volume 88 - Page 427
   2010, Maddy Myers, “Arisia 2010: the Sexiest of Sci-Fi Cons,” thephoenix.com, 26 January, 2010, It’s hard enough to separate the geeks from the creeps at your average Anime con (it’s more of a Venn Diagram than an either/or, really). The task becomes even more difficult at Arisia, where the sexual undertones are … not particularly undertoned.