<p>This came up in one of my groups today. That we could not color bend, or mix 3d printing filaments. I have researched but I am not finding anything talking about Plastic mixing in an extruder.</p>

<p>Why is it that we cannot take say a Diamond hotend, or a hotend with 5+ inputs, and mix any color we want? (assuming all the same type, ABSm, PLA). I think it would be interesting to at the least get a gradient effect on prints.</p>

<p>The best I have seen is natural plastic and a marker system. Or a powder / advanced / out of hobbyist price range process that sprays ink. The only Color Bending I know of is with Recycled plastic that uses multi color. Not quite what I am looking for.</p>

<p>Thanks!</p>

I just started with google and phrase "3d printing color mixing" and on the first place (in fact first two were valueless adverts) I got this
Instructables - DIY Full Color Mixing 3D Printer
.
How it works?
It uses magenta / cyan / yellow filaments and mixes it while printing with Diamond hotend.
It definitely does what you are asking for and it's exactly the same idea you come up with ;)
Overview
Getting the controller board ready for three extruders... I hacked
  a RAMBo board to drive three extruders, however, you can use any board
  you want... (most people use a RUMBA due to it having all the
  pins/components needed for 3 extruders native on the board)
Rewriting Repetier firmware to get color mixing working on your
  machine.
How to install, configure, and use the diamond hotend - tips /
  tricks / lessons learned / etc...
My original Bowden extruder design and various ways to mount the
  three extruders for your set-up
My universal magnetic effector plate and accompanying hotend mounts
  for quickly swapping various hotends. (delta specific)
How to design multi-color models and making STLs that can be
  exported and used as a individual STLs or combining them into an AMF
  file for slicing...
Configuring color mixing in Repetier and Slic3r to print above
  mentioned multi-color models.
Anything else I can think of later that I can't think of now.
Comprehensive overview of Quantum Mechanical Entanglement as it
  pertains to multi-color printing (just kidding, I don't understand
  that... But I will cover multi-color printing throughly)