I'm going to level with you here, be honest, and say that the simplest way to get a graded color effect from a 3D printer is to use a multi-color spool that already has a color-graded effect. But there's a clear drawback to this method - you can’t control at what point within the print that it starts to change color. If such a feature is important to you, then I can recommend the Geetech brand of 3D printers, such as my #1 pick, the Geeetech A10M, my #4 pick, the Geeetech A20T, or my #5 pick, the Geeetech A20M. For more 3D printer information and reviews on the most popular models, be sure to check out all my 3D printer articles. You can access them all here.