I highly recommend the patterns listed on this page as a projects for gradient yarn. I have knitted each of them, often more than once. Each of the patterns is:
Well-written and easy to understand.
A great design to show off a long-colour-change gradient yarn.
Each pattern is owned and distributed by their respective designers or publishers. Links in this page will open a ravelry pattern page, ravelry project page, or other designer website.
The only "design" by coriand3r knits is the Moebius Cowl Seed Stitch which is more of a recipe, based on publicly available tutorials and reference information from excellent knitters and knitting instructors.