Glass gem corn was bred years ago by a part-Cherokee farmer and master seed-saver. Yes, it's real, and, as an heirloom, its seeds will grow true. Today, glass gem corn seeds are saved at Seeds Trust, who anticipate more available next month. Glass gem is an extreme iteration of corn's natural tendency towards different-colored kernels, as each kernel has its unique genetic set for color and size.
Know your soil - do a Mason Jar Soil Test. I did this years ago when I first started gardening. I ended up adding sand to my garden spot. I have had poor soil conditions for the last 10 years or so and have added organic material and composted material to improve my soil condition. The mason jar test is a great place to start.