"the" blue?

Yes, @_undertoad and @CK, "I like THE blue" is what I meant. The sentence makes perfect sense, it just uses an adjective as a noun. For example, "meek" is normally an adjective, but the sentence "The meek shall inherit the Earth" uses meek as a noun and is grammatically correct.

Imagine you were looking at two samples of paint, one green and the other blue. Someone asks, "Which do you prefer?"

You could answer "I like the blue."

In reality, the first speaker meant "Which ONE do you prefer?" and the second meant "I like the blue ONE." Such omissions of unnecessary words are common in English, and natural sounding.

Therefore, when I saw the Spanish sentence, "Me gusta el azul" I submitted both "I like blue" and "I like the blue" as valid translations, because the Spanish phrase could've meant the speaker likes blue in general or likes a specific blue thing.

Well, I understand, but it's not something that I'd say. Whereas it may not be grammatically incorrect to say "the blue," I would always say, "I like the blue one."

I really can't think of any situation where I would actually say this. Even in this context, it seems odd/unnatural:
"What do you like about van Gogh's The Starry Night?"
"I like the blue."

Just my 2 cents...