Blue roses do not occur in nature, so they stand for the unattainable, the mysterious and the wish for the impossible. Dream books read them as longing for something rare.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.