When he sings "there's a certain sadness.
but i know, i know, i know, the sky is what makes the ocean blue."
I think he is comparing the sky making the ocean "blue" (as in a blue mood but also the color blue as well) to sadness, and how there is a beauty to it. Like, the beautiful sky makes the beautiful ocean which is blue "blue". I think he's just trying to get at the fact that it's a sadness with a certain beauty too and things will be alright. I don't think he means literally, or like it's proven that the sky is what makes the ocean blue. I think it was a type of metaphor maybe.
When he sings "there's a certain sadness. but i know, i know, i know, the sky is what makes the ocean blue." I think he is comparing the sky making the ocean "blue" (as in a blue mood but also the color blue as well) to sadness, and how there is a beauty to it. Like, the beautiful sky makes the beautiful ocean which is blue "blue". I think he's just trying to get at the fact that it's a sadness with a certain beauty too and things will be alright. I don't think he means literally, or like it's proven that the sky is what makes the ocean blue. I think it was a type of metaphor maybe.
If that makes sense :)