This is the artwork by Milinje, but resized and adjusted in order to function as a coaster.

We want the top to be (reasonably) flat, but we also want the top colour to fully cover the bottom colour. So I set the top to 2 layers with a layer height of 0.1 mm. In the design, the relief (embossed depth) is therefore 0.2 mm.

While you can print the whole design in 0.1 mm layer height, that isn't efficient. I opted for 0.2 mm layer height overall, but 0.1 mm for the top 2 layers (so that's variable layer height). The coaster is 2.2 mm high, the colour change should be at 2.1 mm. This is how the 3MF file is set up. There is also an STL file in the downloads if, for some reason, the 3MF file is not suitable for you (the STL lacks the layer height info).