Boyfriend's 15 y/o sister coming to me for hair dye

Hey guys, my boyfriend has a sister who is 15 and wants to dye her hair blue. Her parents keep saying no and she keeps coming to me because in the past I've had colored hair (currently black now.) How can I politely and firmly say no? She's been asking for over a year now. Her parents won't even let her dye her tips. I personally feel like it would be nice to let her experiment but bleach is damaging and I'm not her parent. via /r/Parenting http://ift.tt/2oKGH34