Really I don't think parents have any say in how you look and you don't need their permission. You could pose them the exact same question : "how do you stay on speaking terms with people who said they will support you no matter when you are pushing the boundries of what they can handle even though you know you have a lot of changes that are greater in the hopefully not to distant future"?
My suggestion is this. Tell them you appreciate their concerns but what you wear is non-negotiable. They can choose to shut you out or they can choose to be a part of your life. They might not understand what you are doing but that is unimportant. You love them and they love you, and you want to have a good relationship with them. Remind them they said they would be supportive but what they are doing is not.
Though if you are snarky like me you would look your mum up and down and say "your not one to comment on fashion mum"

best of luck Kinkly