"Today's sky is bluer than yesterday's." (Note that yesterday should have an apostrophe, since you are talking about yesterday's sky.) "Bluer" is more natural than "more blue" in most contexts. But there are contexts where "more blue" would be just as natural as "bluer." This goes for the other one-syllable color words you mention.

Bluer. Monosyllabic words ended with an "e" only need to add a "r" to the end of the word.So,here,should be bluer. Polysyllabic words,however,should add a "more' in front of the word. Whiter,redder,purpler,blacker,etc.

In this case, both are acceptable.

Bluer is more common, because one-syllable adjectives usually take the -er ending, but here both can be used.