The color of the school is not material. The facts are simple:
- People, even children, have a constitutional right to freedom of expression
- Schools may intrude on this right where needed to serve the educational purpose of the environment, but no more than the absolute bare minimum necessary intrusion can be tolerated (see the Freedom of Expression Ombudsman's articles on the topic)
- Hair rules, of any kind, are neither minimal nor necessary -they are all unconstitutional and only  survive because they are not challenged enough.
- The cause measureable harm to students - actually undermining the educational purpose of the school.
-To make all this worse, they tend to have racist outcomes (regardless of intentions or the color of the rulemakers)

They are unjustifiable acts of authoritarianism. Opposing them is a good thing.

As for my childhood - if I feel motivated to protect others from the injustices I have experienced, how is this a bad thing ? It's just the golden rule.