Reports differ on exactly when Dartmouth students began wearing caps and gowns, but the tradition appears to have been firmly established in 1892 after at least a couple of years of discussion. According to The Dartmouth of Jan. 5, 1892 (v. 13, no. 8, p. 116): [The class of] "Ninety-two has voted to wear the cap and gown during commencement week. This is the customary English academic dress and has been that of the commencement speakers at Harvard. Recently the dress has been adopted by nearly all of the eastern colleges as the dress of the whole senior class for longer or shorter periods. These colleges include Harvard, Yale, Princeton, Amherst and Williams. Some have adopted the dress for the whole year, some for the spring term, but the majority for commencement week alone. The dress will certainly be comfortable and inexpensive and add dignity to our commencement exercises."
The Dartmouth Ph.D. gown, designed in the early 1960s, is made of a dark green (Dartmouth green) faille with a green pine tree motif embroidered on both sides of the front at lapel level on the black velvet trim. The three bands on the arms (denoting Ph.D.) are of black velvet, the hood is black with blue velvet trim and dark green lining, and the hat is wide brimmed of black velvet (Beefeater) with a gold tassel.
You can examine the Dartmouth Ph.D. cap and gown by requesting Realia 106. For more information about the history of academic dress and what all of those colors, hoods, and trimmings mean, see An Academic Costume Code and An Academic Ceremony Guide, from the American Council on Education.
Best wishes to all Dartmouth graduates!