Huh. That's really strange, then -- I'm at a loss. All I can think is that there's some kind of finish or treatment that's preventing the fabric from taking. If you've got any dye in another colour lying around, you could always toss a scrap in that and see, or try another type of dye, but ... weird. :S
Good luck, anyway!
Therese von Ludowing (Sound Horizon's Märchen)Elsewhere: Journal ~ ACP ~ CosplayLab
Catelyn Stark (A Song of Ice and Fire / Game of Thrones)
Elisabeth - red ballgown (Elisabeth - Takarazuka version)
Thessaly (Sandman - The Kindly Ones)