Special needs or not, individuals must learn to adapt. Just because someone "wants to wear red because it is soothing" does not mean that it is acceptable to do so unless red is included in the uniform guidelines. If wearing a collar feels like "cut glass" then I'd say such an indidual has such significant issues at hand that perhaps they should not be in a public school at all. Life is about adapting to the rules/laws set forth by society. Perhaps if children start learning this at an early age through something as simple as wearing a uniform, there will be fewer instances of nonconformity and strife in the future caused by individuals who feel it is their right to "express themselves" through breaking the rules.