Clear plastics don't let diffuse colors through...sometimes

[Speedster]

These may help. 

1)   Be sure the entire model is lifted just a tiny bit above the ground plane.  This should kill the black shadow.

2)  Make sure there is no contact between the inner components and the jar.  Use scaling on the jar, about 1.002 or so.

3)  Be sure to uncheck "Global Illumination Cache" on the Render > Options tab, way at the bottom.  For some reason this plays havoc with clear and cloudy plastic.

Bill G

[Peter H]

Thanks for taking the time to reply.

1) I'm not having a problem related to the black shadow at the bottom (though I appreciate the tip.)
2) There is no contact - I always build with tolerances for paint and assembly, so that is not an issue.
3) Unchecking or checking "Global Illumination Cache" doesn't change the problem.

[Peter H]

Will, I've sent you some files via WeTransfer.