From Elann:

Two-sided eyelash yarn with the look of glorious feathers - wear it in pristine white, or dye it to your own specifications!

To dye 100% polyester yarn to your own specifications, elann.com highly recommends PROsperse Disperse Dye from Pro Chemical Dye. The Pro Chemical website offers excellent instructions, and their disperse dye starter kit, which includes everything you need for professional results, is just US$11.95.