The phrase "subtle undertones" is correct and usable in written English.
You can use it when you want to describe a feeling or suggestion that is present in a situation but not easily noticeable or detectable. For example, "There was a subtle undertones of resentment in the conversation between the two friends."
The double-bassist Aaron Baird added subtle undertones to the 15 short "Scenes From a Novel" that closed the recital; the violinist Jennifer Choi played with intensity but a lack of color, compared with her colleagues.
Narrated in a firm and objective manner with occasional subtle undertones of humour and irony, Freeman's stories were deft character studies of somehow exceptional people who, trapped by poverty or other handicaps in sterile, restrictive circumstances, react in various ways against their situations.
I loved the subtle undertones of the piece too, the way it's clearly relevant to our times today".
Subtle undertones of galangal (a type of ginger), lemon grass and kaffir lime leaves provided the perfectly balanced seasoning.
When grilled, the meat is slightly flaky and quite flavorful, gamey, though similar to a quality cut of beef, with distinct yet subtle undertones recalling its marine origin.
(Who's the subordinate little puppy now?) Your hands are slickly wrapped, and your mouth is sucking his cock faster but with subtle undertones of a gentle coaxing.
It was not right at all; engrained stereotypes, the thoughtless use of words and pictures with their subtle, insidious undertones.
A subtle undertone of sulphur.
You will detect a subtle undertone of dried pasta if drinking water.
Just as tangerines begin to go soupy if left in the sun, there is always a subtle undertone of decay in fruit perfume; wearing one can be like grafting a memento mori painting directly onto your body.
But since you are in Tesco and you may feel like splurging, I suggest Moscatel de Valencia (16 points, £3.12), which has silky honey fruit with a subtle undertone of marmalade.
