Altar Boy Cassocks

For the feast of Pentacost, the altar boys....er, servers....wore red cassocks. Is that OK? I just assumed it was, but here's what Father Z has to say about it:

"This is a matter of aesthetics.   Back in the day colored cassocks were tolerated by the Sacred Congregation for Rites.  To my mind it is a thing of fairly small importance."

I wonder what he would say about the boys from Our Lady of the Snows in (of all places) Sri Lanka?

 I think it would be cool if they were discalced.