Learn Icelandic: Í myrkrinu blikkar vitinn ýmist rautt eða hvítt. - In the darkness the lighthouse flashes sometimes red and sometimes white.

This correlative conjunction phrase translates to "sometimes [A] and sometimes [B]" or "alternately [A] or [B]". It is used to show that two states or actions happen in alternation. Here, it links the two colors rautt and hvítt to show that the lighthouse constantly switches between flashing red and flashing white.

Why are rautt and hvítt in the neuter singular form instead of matching the masculine noun vitinn?

In this sentence, "red" and "white" aren't acting as adjectives describing what the lighthouse is; they are acting as adverbs describing how it flashes. When you use an adjective as an adverb in Icelandic, you almost always use its neuter nominative/accusative singular form.

Why is the word order blikkar vitinn (flashes the lighthouse) instead of vitinn blikkar?

This is a classic example of the V2 (verb-second) rule. Because the sentence begins with the prepositional phrase Í myrkrinu (In the darkness), the verb blikkar must immediately follow it to remain the second element in the sentence. This pushes the subject vitinn to the position right after the verb.

Why is there no 'u' in the middle of myrkrinu if the dictionary form is myrkur?