When to use ещё and when to use пока?
С утра пока темно.
С утра ещё темно.
Is there any difference in the meaning in these examples?
EDIT:
As @Alex.S said, there is also one other variant:
С утра пока ещё темно. So, what are the differences in the meaning if they exist?
The first sounds like an unfinished sentence, like a clause because пока in your sentence means while.In the morning while it's dark or while it's still dark...(С утра пока темно...or С утра, пока еще темно,я готовлю завтрак).
The second is OK.In the morning it's still dark. It sounds like a background for a story. Пока and еще have got several meanings. The main are: 1.at the moment, now, waiting for some time.
Я пока подожду. Пока мне ста рублей достаточно.
2 пока еще or пока--still, yet
Пока еще ждем.(we are still waiting).Пока еще не уехали.(we haven't left yet.)
3.пока--while
Куй железо, пока горячо.(Make hay while the sun shines)
4пока--until
Сиди здесь, пока не приду.(Stay here till I come).
ЕЩЁ, 1. (ещё). --again
Ещё раз.
(ещё) --in addition с предшествующими союзами, и, да.
Дайте мне масла, муки и ещё сахару. Он способный, образованный, да ещё добрый. | Он мало способен, да еще ленив.
(еще). already
Дом сгорел еще в прошлом году.
4.еще--still
. Молод ты еще, чтоб курить.
5еще--having enough time
. Я еще успею на поезд.
Она стала ещё красивее.
С утра пока темно. = Not a phrase. As has been mentioned, it looks like "In the morning, while it is still dark...", requiring a continuation. And a comma before пока.
С утра ещё темно. = In the morning it is still dark. Means, well, it is still too dark in the morning for the proposed activity.
С утра пока ещё темно. = It is still dark in the morning in this part of the year/season. Means you need to wait some months for it being not that dark in the morning.
Roughly, "пока" is closer to "yet", whereas "ещё" is closer to "still". "Пока" implies continuation: С утра пока темно[, но скоро будет светлее]. You can even combine these words, to make the opposition even stronger: ...пока ещё темно, [но совсем скоро уже будет светло].
С утра пока темноIt sounds more like "In the morning, while it was still dark, [someone started to do smth.]". I guess native speakers could say this from time to time, but in fact it's a speech mistake.