Eyeglasses made of nylon were introduced in the late 1940s. Because of brittleness and other problems, eyeglass manufacturers switched to blended nylon (polyamides, co-polyamides, and gliamides). Today's blended nylon frames are both strong and lightweight.
If you want the colorful frame then zyl (zylonite, or cellulose acetate) is your material. Zyl is a very cost-effective and creative option for eyewear and is extremely lightweight. Particularly popular right now are laminated zyl frames that have layered colors.
Some manufacturers also use cellulose acetate propionate, a nylon-based plastic that is hypoallergenic. It's lightweight and has more transparency and gloss than other plastics. If your main criterion for a frame is lightness, then definitely consider propionate frames.