This is another take on the idea of sunshine: Creating dual-color filament. 

Inspired by a video of stefan (CNC Kitchen) I wanted to try this myself.

In differentiation to those above: This shall be an accessible approach for those who use onshape and want to play around with it/ the parameters. And as you can see from the pictures: Printing the filament and printing a model worked great.

Give it a try for yourself, however be aware that those spirals create superbig stl-files. If you can, import the STEP files in your slicer. You can modify the onshape model with the provided variables: 

One hint though: go slowly, dont overdo it as your slicer might crash from the big filesizes. 

In the slicer you select the middle layer for the color change.