I think, like most things, it depends on the child and how tastefully it is done.
I would worry about dying/perming young children's hair cos the chemicals are so harsh and their skin so sensitive but you can find some organic/natural products on the net these days.
I think ear piercing is a slightly more grey area....i don't see anything wrong with a little girl in a beautiful little dress ( Laura Ashley etc) and tiny little sparkly pink studs and mary jane shoes, especially if she is a girly girl like my one is (who doesn't have earings I have to say) and a child wearing inappropriately adult clothing, huge hoopy earings, greasy red/blond streaks and generally not looking very beautiful. That makes me feel sad.
I encourage my girls to look beautiful and tell them that they are so and if they want to experiment with make up/hair products, I try to let them under my strict guidance and supervision so they can have the experience in a safe way. Most Girls want to learn about these things that they see us use all the time. My 12 year old now, takes very good care of herself, still wears very pretty/beautiful clothes and gives herself manicures/pedicures/looks after her skin etc and if she wanted to colour her hair, I don't think I would object as long as it were tasteful. She also has a healthy body image and good self esteem.
I fully sympthise with you Pippa: in your situation, if there were something about my child that really bothered them personally and was becomming a thorn in their side, I would help them to find a solution as this is what I would like someone to do for me.