Are you referring to E! Entertainment Channel's slogan? This is not a common expression, but it seemed to me that "pop" was used here in the same context as e.g. "pop" of colour. Pop of colour means that a patch of colour really stands out from the background e.g. a pop of red on an otherwise dull grey dress. Therefore, "pop of culture" is probably supposed to give the impression that E! provides entertainment that really stands out from other channels?

In that context it has no real meaning, it is just a play on words. The author was trying to use "creative" heading in the article, like the "Weird Science" heading, when she talked about the scientific reasons Hawaii has more rainbows.

Yes, actually, it is a title of an article about Honolulu's rainbows. How much they are valued inside the culture.

Are you sure you didn't hear 'popular culture'?