It is mentioned in a book by ISKCON that red hibiscus flower is not offered to Krishna. When He has created this beautiful flower then why not offer it to Him?

Krishna is Bhava Grahi Janardhana. He has even accepted a banana peel from Vidura’s wife. Without the basic principle of bhakti or devotion, nothing can induce the Lord to agree to accept anything from anyone. Make sure you offer everything to the Lord with love and devotion. Usually these general rules are mentioned in the scriptures to guide us. We hope this is all right with you.