State vs action

In a unit about until and by in the PEU says:

We use until to talk about situation or state that will continue up to a certain moment. We use by to say that an action or event happen at or before a future moment.

Are there formal differences between state and action? I think when we talk about something we can refer to state as perhaps longer action and to an event say that an action is shorter regarding to the longer action. So I suppose we always talk about these two action together. It is true?

I looked up Swan's PEU, it's Topic 602.6, "until and by: states and actions".

I've come up with these examples:

The sky will be blue until 9 p.m.
The sky will turn black by 10 p.m.

"The sky will be blue" describes a state. The sky is not doing any active action to keep its blue color.

"The sky will turn black" describes an action: the sky is changing its color. At some moment before 10 p.m. it will become black.

But I guess the boundary between state and action is blurred:

The sky will be turning black until 10 p.m. (here, a slow action is seen as a state or condition, IMHO) The sky will be black by 10 p.m. (here, an action is implied but not named)

• Let me ask you one more question. When you said I've came up with these examples..., what was the meaning of came up you mentioned? I've found dictionary.cambridge.org/dictionary/british/come-up and suspect it's to be mentioned or talked about in conversation Oct 22, 2014 at 3:16
• @DmitryFucintv --- Come up with - "to invent, create, or think of" - "I don't know the answer, but I might be able to come up with a good guess." Oct 22, 2014 at 3:19
• @DmitryFucintv - and I've committed an error in writing it as "I've came up": one should use only "come" (Past Participle) after have. "I've come up with examples". Oct 25, 2014 at 10:29

The state represents a condition of something. Example, the car will continue to idle until the gas tank is empty. You may stay up until 11 PM. By midnight, you must be ready for bed.

Action example. Wait behind the door until Bob walks in.