Roses are red is something we can’t really quibble with, always providing we are talking about red roses, of course. The Queen of Hearts might prefer it otherwise but no one would expect white roses to be red. Just the assertion that roses are red is quite enough to establish that we are talking about red roses. My love is like a red red rose doesn’t cause any problems, there are red roses that it would be very complimentary to be likened to.
If any one should ever liken you to a red, red rose it would seem churlish to enquire as to the variety. Especially if the phrase is being used in a poetic sense, so that some license should be given. It is after all, well known that all poets have a license to make things rhyme at the expense of solid fact. Solid facts tend to be prosaic and therefore not inclined to fit with the meter or to have conveniently sonorous synonyms or even, if all else fails an antonym with sufficient sympathetic syllables.
Still there are some things that must give, even poets, pause. To say that black is white may have its uses in marketing and advertising and may be essential in the real estate business. To call all cats grey in the dark, may be acceptable to all who are not cats. But violets are blue?
If we’d called them blues instead of violets, would we say blues are violet?