I changed material to a Toon material, and when I changed the color to one of the RGB (to make RGB mask) it became transparent.
The transparency parameter in your case is 1.
Zero should be solid.
Great!
Do you have an idea why when the Counter Width is 0 the whole object with this material becomes black?
hmm, sorry - I can't explain the "why", but if you switch of the interior edge contour, then all parts appears in color.