Q. Do different colors of roses have different meanings?
Thank you for sending us this interesting question. Part of the problem that you are running into in searching for a definitive meaning to flower species and colors is that it is not a scientific concept but a matter of interpretation. There is a long history and many traditions that relate to this idea and thus many valid interpretations. While there had always been a strong tradition of floral symbolism in Western culture, the impetus for its resurgence in Europe during the late 18th and early 19th century came from the East. The Turks had a tradition called Selam (sending a greeting encoded in flowers and objects) that was eagerly adopted by the French. The Eastern tradition was based on rhymes and cultural associations that lost their meaning in translation. In the hands of the French, the language of flowers became increasingly symbolic.
New York Botanical Garden has a guide to The Language of Flowers that will help you to better understand the history of the concept. You will need to decide which tradition you wish to base your interpretation on, no one association being more valid than another. There are numerous books in the NYBG library dating back to the mid-19th century on the subject should you wish to do some research here. Let us know and I will put you in touch with a librarian who can help you with finding the right books.
I hope that helps.