Someone's hair colour, style, or body mods to not reflect who they are as a person, their capabilities, or what they will be like as an employee. Most places will not hire you if you have hair colour that looks unnatural, a haircut considered extreme (like a mohawk or a man with long hair), if you have visible piercings or tattoos. Why? For no other reason than it is unappealing to many people and because some people assume people that look like that are degenerates/delinquents with bad morals. That is discrimination. An obese person may not be appealing to many people, but that would be discrimination to not hire them for that reason. One may argue that customers won't shop where a person who has tattoos/piercings works. Well in this world some customers might avoid a place because an employee is gay. So why is one illegal to refuse a job to and not the other?
Appearance does not reflect character, capability, or morals. To not hire a person with piercings/tattoos or dyed hair for worry that they do drugs or might steal from the establishment and would scare away prejudiced customers is just as prejediced and discriminatory as not hiring a black person for the prejudice that they would steal and scare away prejudiced customers. It is discrimination and it is WRONG.
We understand, a customer finding a dropped nose ring in their food can result in law suit. A piercing can be dangerous in certain jobs. I would understand certain industries wanting employees to remove piercings to remove health and safety risks or if a person had an offensive tattoo like a swastika or something witha swear on it and this tattoo is not covered by clothes. But hair style/colour and tattoos are in no way a threat to health or safety. Long hair can be tied up/netted. Dyed hair and tattoos do not affect anything other than appearance. Nothing about a person's physical appearance should be expected to change unless it is a health and safety risk. If employers want appearance changed for no other reason than for the appearance of the change, it should not be allowed.
Discrimination laws officially protect those of a certain race, religion, age, gender, marital status, family relation, and more recently sexuality has been added to that list. Let's add physical appearance to that list, including piercings, tattoos, and hair choice with the exception of threat to health and safety.