These were the quickest pictures I could find to demonstrate the effect.
The one showing the hand is front-lit, the dots are highlighted & reflect the light back creating a more opaque effect.
The one looking out the window is backlit, so the frit creates shadows and fades into the background.
Distance from the frit has an effect too; closer = more transparent, further = more opaque.
On a boat, the backlit (transparent) view would be from the interior looking out, while the front-lit (blending) effect would be from exterior looking at the hull.