I'm trying to render a simple cosmetic lip balm tube. The body is made of blue and white plastic, while the overcap is made of clear plastic. When I produce a render, the overcap makes it look like the parts of the tube inside it are a very dark grey colour, when in fact they are not. When they're rendered individually, they look accurate, but when together the clear overcap obscures the white object.
The clear cap is a basic material which in the BSDF settings has transmission set to 1.0, IOR set to 1.1, and roughness set to 0.2. I believe this should make it like glass with a high level of optical transparency.
In Render Properties > Light Paths > Caustics is enabled for reflective and refractive.
I tried adding an additional light (a sun) but all this does is blow everything out except the top region I'm trying to illuminate.
I've attached a photograph of the real object. As you can see, the cap is crystal clear, and the internal coloured components are easily visible.
I am sure this is a simple fix. What am I missing?