I use those all the time and I haven;t had any issues, even with light steaming during ironing. I can't make any promises for you with your own situation but I would definitely say that like Vanessa said, either do this piece at home only, or get colorfast threads if you want to take your project places. Whatever you do, I wish you the best of luck and I am sure your piece will be really beautiful.
My Work in Progress: Just Nan Bellemeade, Mirabilia Autumn in My Garden
My Completed Miras: Mermaid of the Pearls, Queen Mermaid, Waiting For Ships, Deepest Love, Shimmering Mermaid, Emerald Mermaid, Summer In My Garden, Spring In My Garden, A MIdsummer Night's Faerie, Lilly of the Woods, Christmas Elf Faerie, Winter In My Garden, The Woodland Faerie, Easter Faerie, Halloween Faerie, Enchanted Mermaid, Titania; Queen of the Faeries, Miss Valentine, New Years Eve Fairy, Thanksgiving Harvest Fairy, Fairy Moon
My completed Passione Ricamos: Galatea
My Webshots folder: http://community.webshots.com/user/emilyaliu