There's apparently a verse to the song Lavender's Blue that has this:

Roses are red, dilly dilly
Violets are blue
'Cause you love me, dilly dilly
I will love you.

There's also a not-very-kind version of "Roses are red" that goes something like this:

Roses are red, Violets are black.
Why is your chest as flat as your back?
Haven't heard it since maybe fourth grade, which is about the same maturity level...