Sorting Cupboard

Near the back of the bright, icy entrance hall is a small black door, with a tiny, square, stained glass window set into it. The dark blue patterns of glass in the window change toward the middle, where the delicate panes of thin material - now suddenly such a light shade of blue that it's almost white -mold into the shape of a complex snowflake. Inside the door is a small black room, with just enough light for a single chair to be seen, along with a silver pedestal. The pedestal is emitting a small glow, and atop it is a flat surface, with a dull, stone rune embedded lightly into it. Students are sent into this strange room one at a time. They place both hands tightly on the rune, close their eyes, and make their mind blank. After a second or two, there is a chime, at which the student is to open his or her eyes and look at the rune, which will be glowing either red, blue or yellow...