Hmm... the description says "Brightest on natural fibers such as cotton, wool, viscose, rayon, and silk," but dyes often stick better to either protein fibers OR cellulose fibers. You might try something like these acid dyes which I think are intended for wool and should work well on silk too. Or try using Kool-Ade, but I've read that's hard to find in blue?

One of the chemistry teachers at my high school ran an annual tie-dye lab and used procion dyes, but those were for cotton. My dyed tee shirts are over fifteen years old now and still are eye-catchingly bright.

(The beanbag chair in the background was bought, not made.)