From a commercial site:
"The weave of dupioni silk contains minor irregularities. These are characteristics of fine silk yarn and should not be regarded as faults. Dupion silk is dyed and woven by hand and consequently the colors may vary slightly from those of the sample.

Vegetable dyes are used in the dying process to compliment the natural silk. These dyes, however, have a low light fastness and consequently fading will take place when the silk is exposed to strong, natural and artificial light. To enhance the lustre and to help protect the silk we strongly recommend that all curtains and blinds are interlined."

Hmm--shouldn't that have been dyEing process?