https://www.youtube.com/watch?v=mATq64vEDm8 Using the S3D processes and with some tricks it's posible to force the layer order and reprint on the same spot on a precise order to get semitones from just 2 extruders. Basically check the FFF s3d process of example, they work Different materials mix different, for example a semi transparent PLA will have less density when mixing with a opaque material. 50% + 50% won't give you the exact semi color, it depends on the density of material of the filament used. For this example I'm using BCN3D White PLA and Silver PLA. Using other colors will change the colors. Also, is VERY important to have the best possible calibration. On BCN Sigma fine tunning it's very easy using the menu control, no need to redo the print calibration, but I still need to make a simple colormixing calibration print to do the fine tunning, because when one tries to print on the same spot with 2 heads to get the best repetition possible it's important to have more than naked-eye calibration. For most materials the right amount to mix of flow is always higher than just 100%, 120% total mix (40-80 / 100-20 etcetc) will give better colors. Also beyond 0.12 0.14 layer height you might get a more 'lines' effect between layers, the thinner the resolution the better the color lies to the eyes. OFC it's very hard to get perfect colors, sometimes it just depends on the materials, some mix better or worse, but specially the flow depends on the color density of the material. Check the S3D processess and have fun. Tips Using 0.1001 instead of 0.1000 will force that process to print 'after' the other. This means that you can force even better the 'order' of the colormixing. This is very important to get a constant semitone. You can avoid printing infill for one of the color mixed, but I prefer to print at least 5% to just get a more even cooling for a small object. Play with this as you see fit. On S3D the FIRST process will fit the FAN speed. Don't set fan speeds for any other process than the first to print on the bed. This way you will avoid that the fans go on and off, this is important to get a constant air flow and avoid stuttering the boards with way too many instructions on just a second, because S3D see's each process as 1 print, so when goes from A to B process if B has new fan settings it will start the layer count from 0.. Complex? Yeah a bit, but I got use to. Models used on the S3D Files World with Stand by MosaicManufacturing https://www.thingiverse.com/thing:224... Multi-Color Living Room https://www.thingiverse.com/thing:152...