Learn English – What does “barely” imply

For both of your numbered examples, I would expect that "blue" is the implied base color. For the sky, blue is the obvious choice; without a further specifier such as "pale grey", blue pretty much has to be assumed. For eyes, a wide variety of colors may be possible, but blue and brown are the two primary choices, and of the two, "pale brown" would not be written as such (it would be "tan", or "tawny", or "hazel"); and any other base eye color would be unusual enough to be specified: "pale green", "pale bluish-gray", etc.

This is a really complicated question, and the answer is not simple. This phenomenon involves Negation, Quantification, and Metaphor, and that's already too much for a short answer. I'll try, though.

The words in question are called "approximatives" in the trade. They are adverbs of degree, I suppose, if one must put a POS tag on them, and they function to add some precision to quantification. What they mean generally depends on what metaphor they're instantiating.

It's like calculus -- how to describe precisely the experience of approaching some kind of limit in a continuous event or state. Without math. This is not easy, so we use metaphors instead.

There are several kinds of measured continuity that humans naturally experience, leading to several kinds of natural metaphor for humans measuring continuity. They can measure, as it turns out, linear motion (JOURNEY metaphors), or they can measure accumulation (CONTAINER metaphors).

• Motion metaphors: Personal Experience (LIFE) is Personal Motion (JOURNEY)
  • (There is a directionality to this metaphor, so these all imply not there yet)
  • almost/nearly/practically at the 50-yard line/goal/limit/right age/border
• Container metaphors: LIFE is Accumulated Memory (CONTAINER)
  • (think a big jar of memories, piling UP as they get MORE -- a vertical linear model)
  • pass/over/under/up to the mark/the top/the time limit/two years/ten million rubles
  • (or think a cupboard full of memories, which may be full or bare)

So, one point is that these are both vectors -- they have a starting state (BEGINNING, EMPTY), they have an ending state (FINISH, FULL), with a continuous range between them, and the directionality is one-way (FORWARD, UPWARD). That means that purely locative phrases like near or close to mean "not yet" only if they're interpreted as directional metaphors; it isn't intrinsic to their meanings.

A second point is that some of these terms are intrinsically negative, and can trigger NPIs like ever. Let me just say that this does not make the grammar any simpler.

• I seldom/rarely ever see them.
• He hardly/scarcely ever gets it right.

A third point is that there is a personal and temporal dimension to these metaphors. Abstract concepts like emotion and time are almost impossible to talk about without metaphor, and they permeate almost all our metaphors.