I guess that I should have prefaced the first reply with "As far as I know..." I was speaking from my own experience, my Ph.D. hood has my school colors on the inside and the blue on the outside. It's been a long time since I looked at it. The last time I did there was a spider living in it. Also my recollection of the other colors (I guess that the dentists get the yellow) was from my commencement several years ago.
Geo