Meanings of deep undertone in English

And the rumble of an occasional passing cab came like a deep undertone of peace.

I saw it with a deep undertone of feeling; for it was the last I should behold.

The sheer walls of ice glowed with a luminous, unbelievably rich blue light that had a deep undertone of green.

And there was a deep undertone of excitement that gave them a magnetic power that they could not have in quieter moods.

The cigar on the opposite side of the little table glowed rosily several times, and then Quimbleton's voice resumed, in a deep undertone.

Her voice had the high lilt and the deep undertones of the Forest.

"What does the man mean?" he mused in deep undertones.

But hardly any less disquieting has been the unleashing of sentiments which scarcely concealed deep undertones of prejudice, hostility and even racism.