You know.. I have a multi-material mixing print head.  Perhaps I should actually use it.

So I did.

No actual active mixing, but I programmed the change from white to black at least.  I somehow found I could spare the time required for adding 2 lines of gcode (M163 filament percentage commands for the curious) at a layer change... mostly.  Well.. I liked the idea of the M163 command, so I implemented it within the guidelines of the actual standard.

<RANT> 

My implementation uses non reserved characters...  yes, gcode actually has rules people.... and it is 100x more precise.   I use a range of 100.0 to 0 instead of 10 to 0.  It doesn't matter much here as the swing is from 100.0 to 0, but your get the point.  Yes.. you may have assigned meaning to this Mcode definition, but in the process you used characters (in a very simple system) already assigned to other functions cause they fit your mindset..  And now we are all screwed.

Sorry.. but coming from the 'other side' I'm annoyed at the general RepRap movement not following the rules.  

But hey... usage equals reality...  Um... No.  

Standards exist for a reason.  If you want to deviate, use the built in variables which allow for deviation, or define your own system.  Don't call it gcode unless systems designed to read gcode can actually do so.

Bastardizing existing standards sucks, and I simply refuse to adopt that kind of M$ mentality.  Well... I have to admit M$ has been getting a lot better at this in the last few years.  But...

 You know how many hours I've spent of my life working around the stupid little changes "companies" have made to established standards, simply because it was easier or they wanted to add feature X and didn't want to do the associated work required?  I actually have no idea...  But I can tell you that I lived through the early days of the internet and that I still deal with this kinda crap for my "real job" on daily basis. Compared to actual problem solving, working around silly choices like these consume an absolutely huge portion of my time.

So... I have chosen to implement something within the existing standard.  I had to change one character.... 

Now is the time.  Resist!

</RANT>

Anyway....

White to black is one of the things that the M2 does exceedingly well.  No thought or planning involved.  The sheer density of the pigmentation of the black filament takes care of everything.

Going from black to white... that requires actual planning.

So now I have the perfect light ring.  You can paint yours.  :)