Flowers for Lord Shiva

Are red flowers okay to offer to Lord Shiva? My priest made me place a red flower at the feet of the Shiva statue at the temple and I asked him if he was sure because I had read that it was not okay. He said it was fine, but there are lots of articles online saying it's not okay. Thank you. If it's not okay, can you explain why and what I can do to rectify what I did?