Does she dye her hair? Has she ever in the past and just doesn't now? Dying hair is damagjng, so if she has stopped and is keeping her hair natural, you need to respect that. As for bringing it up, just do it. "What do you think if red hair? Have you ever wanted to try it?" Keep the conversation far away from her current styl, you might insult her, but talking about what ifs should be fine. Also, you need to know that red hair is hard to get right. If you're fine with that purple color thend it's easy, but if you want a copper red it's hard. I've been dying my hair red since 2003 and for the past two years have stopped using grocery store boxed dyes. Let me tell you, when I dye my hair copper first I have to lift the previous color (smells awful) and then dye it, I add a red tinged protein filler to my conditioner for washing it. But even with all that?the red fades fast. And it is stupid expensive to get it done professionally. Good luck, and if she decides to go red, I hope you really appreciate the effort she's taking for you. To note, my husband is color blind and prefers blondes. I would never go blonde, it would make me look awful, so just remember that ultimately her appearance is her choice and she probably knows what colors look best on her.