Like, If you want to say "this movie had liberal themes that weren't that obvious, but you can tell If you pay attention." I think the word I'm looking for starts with "sub."
subtext 1. An implicit meaning or theme of a literary text. 2. The underlying personality of a dramatic character as implied or indicated by a script or text and interpreted by an actor in performance.
subliminal might be what you're looking for...
*existing or operating below the threshold of consciousness; being or employing stimuli insufficiently intense to produce a discrete sensation but often being or designed to be intense enough to influence the mental processes or the behavior of the individual: a subliminal stimulus; subliminal advertising.
I think what you might be looking for is subcurrent (or undercurrent):
Definition (via Oxford Dictionaries Online):
An underlying feeling or influence, especially one that is contrary to the prevailing atmosphere and is not expressed openly.
The buoyant mood of his audience was certainly out of kilter with the deep undercurrent of frustration evident elsewhere in Bournemouth this week.
Perhaps the simple 'subtle' would suit your meaning. Any of the following senses might fill the bill, although the first seems closest:
1. not immediately obvious or comprehensible.
2. difficult to detect or analyse, often through being delicate or highly refined: a subtle scent.
3. showing or making or capable of showing or making fine distinctions of meaning.
4. marked by or requiring mental acuteness or ingenuity; discriminating.
(Collins English Dictionary – Complete and Unabridged, 12th Edition 2014. S.v. "subtle." Retrieved April 26 2016 from http://www.thefreedictionary.com/subtle )