That is #665, nonth panel, right after Roy's resurrection. Vaarsuvius is still paralyzed and drained, and somebody removes her cape to temporarily cover up Roy. We can only see half of a head and one arm of Vaarsuvius though. Vaarsuvius gets her cape back before her next appearance in #667.
the feather in Belkar's hat, but nope, that's not blue.
Update: heck, even the quill provided to Vaarsuvius in the library of Shojo's personal wizard is not blue. It's strange to see a red quill in Azure City.