No matter how much you try defending it, this is bigotry, plain simple hate filled. The root cause of teacher's / college administration is hate for these students' faith.
The teacher's role is to educate the students, not select and reject based on their outfit.
As far as your uniform argument goes, if there is something missing it stands, but if there is an addition to it due to one's circumstances it is acceptable. If these students are wearing the required color dress and shoes, they are not violating any uniform dress code.
A Hindu female student may choose to wear a tilak or a male student may choose to wear that raakhi thing ........ how different is this from that?