Coaster with Venn 6 rings. Each ring is .4mm apart from each other so you can change out the colors every .4mm to display all the colors of the rainbow. My suggestion is to start with black, change out to yellow, then Blue, Red, Green, Purple and Orange, then back to black for the top.
Each ring is .4mm apart from each other. I built it in slic3r and broke up the file into 8 pieces based on the height of the print. I started with black and then switched to yellow when the print started at 2.350 mm z, Blue at 2.750, Red at 3.150, Green at 3.550, Purple at 3.950, Orange at 4.350, then back to black for the top at 4.750.
Layers are 0.2mm height. bottom layer 0.15.