Les violettes sont bleues.
However, this phrase is not typically used in French because:
* Violets are not actually blue! They are usually purple.
* The phrase "violets are blue" is often used in English as a starting point for silly rhymes and sayings. This type of humor is not as common in French.
So, if you want to use the phrase "violets are blue" in French, you would have to explain the context. For example:
* "Dans la chanson, les violettes sont bleues." (In the song, violets are blue.)
* "C'est une expression anglaise qui veut dire que quelque chose est faux." (It's an English expression that means something is false.)
If you are just looking for a way to say that violets are purple, you could say:
* Les violettes sont violettes.
* Les violettes sont mauves. (Mauve is another word for purple.)