I heard when R’ A. Feure was young he got a call to speak at a dinner, and during the call the caller indicated they wanted him to speak only if he’ll wear a ‘Frak’. His father-in-law, R’ M. Gifter z”l, told him he shouldn’t speak for a mosad that’s not ’emes’.
If one person happened to be seated there wearing a blue shirt it shouldn’t sound any alarm and it shouldn’t diminish the Yeshiva’s good image in any way. On the contrary, I think caring about these externals in such an extreme manner is far far worse than 10 guys wearing purpal shirts…