I have to disagree that this is a good thing. The college sounds like a private school, and as a private entity should be able to set their own dress code. If it's a public school(doubt it, given the name) then the ruling is probably the correct one.
It is private. Usually* they are allowed to set their own dress code.
However, Ms Haddad would have been forced to wear a headscarf because she is Muslim. Would she have been Christian, then the school would allow her to choose. The school employs more female Christian teachers. This inequality between Muslim and Christinian is what the Equality Commission deems illegal.
* The Dutch education system has both private and public schools. Most private schools are 'standard' Catholic or Protestant, Islamic schools are on the rise, and a range of other flavours also exist. Private schools have a constitutional right to be equally funded when compared to public schools. When a group of parents can show that they are enough students in an area to found a school of a type which doesn't exist in that area already, the government is forced to fund such a school.
Public schools have to accept every child who applies for the school. Private schools have the right to refuse them, if they or their parents don't have the right religion. In practice most Catholic and Protestant schools don't refuse anyone. In some urban areas there are Protestant schools without Protestant students. It is hardly visible that these schools are Protestant.
And now to the dress code. Public schools cannot set one. At least not on religious grounds. Some Catholic and Protestant (private) schools with a majority of Islamic students have tried to ban headscarves, for religious reasons. Without success, because courts decided that they were only Christian in name. However, a Catholic school with a more traditional Catholic identity, which also selected their students (they have some Islamic students though) had more success. They were allowed to ban.
Also (for example) more orthodox Protestant schools and Islamic schools are allowed to set such dress codes. As long as they don't discriminate between religions.
