In what manner does Fusion support color information in exported STL files?

[personflakes]

I maintain an STL decoder, and have been trying to hunt down files representing edge cases and nonstandard features.  I am not a Fusion user, and I have no access to it.

I have run into a handful of STL files which were ostensibly made by Fusion 360.  These are binary STL files, and they have 'COLOR=' tags in the file header along with an embedded uint8 RGBA tuple.  This appears similar to the format used by Materialise Magics for encoding per-object color.  I want to know whether Fusion also supports the same 'MATERIAL= ' header tags that MM uses, or whether Fusion also supports per-facet color information in the same manner (if at all).  I have not found any examples, but it's essentially impossible to search the web for such a thing.

Is this behavior publicly documented anywhere?  Does anyone have an example STL which demonstrates either per-facet color or per-object material (reflectance) information?

The complete impossibility of web searches suggests that I must clarify:  This is not about trying to bludgeon STL into a multicolor 3D printing workflow.  This is a question about nonstandard features of the file encoder.

[TrippyLighting]

I have reposted this on the EE Slack channel where we (Expert Elites) have direct access to the Fusion team.

I provided a link to this thread. With a little luck we'll get some feedback here. It might take a while though!

[personflakes]

Thank you for the connection.  I'm not exactly in a hurry.

[personflakes]

Any updates on the crosspost?

[TrippyLighting]

I've got some replies, but noting conclusive yet. 

Usually .stl does not support colors, so I guess the question is why the exported .stl include these tags included, even if they aren't used. Someone answered:

"Years ago we added non standard  color  attributes to bodies in inventor. This seems to have made its way into atf. I know it used to be true that fusion did not export color and inventor users asked us to add it. This could be how the current support came to be. If I remember correctly multiple other CAD apps do this as well."

I don't know what "ATF" is and have asked for more feedback ...

[personflakes]

I'm not sure what it stands for, but it's part of the header text. For example:

'STLB ATF 12.14.0.127 COLOR=õõöÿ'

Seems to be

STL (binary)

Encoder or library abbreviation and version number?

Object color = [245 245 246 255]

Not sure if the encoder ever puts these header tags in an exported ascii STL (or whether it can export ascii STL) ...