I have a jpg attached, and the transparent color is set to black:
Oddly, I just realized only civil3d has that property available.
So I opened the quickwatch in visual studio on the raster object and happened to expand the xdata item.
Look what I found!
Can you believe it, adesk is using xdata for the transparency color, whoohooo!
What a fluke I found that. The 0 is black, but is a different number if you select some pixel in the image.
Guess I answered my own question while writing this.
Not sure why vanilla acad seems to be missing the property in browser, the xdata is still there though.
Xdata is a bit easy to erase on accident, but honestly I would rather they add new features this way than modifying the core entity definition and force new dwg version.
