The first part , the one that has translucency and also no translucency, before you add it as a component,
Is that an assembly ?
This is a bit complicated, :
"earlier versions" ( "NX lower than version 12 something") Display changes applied in sub assemblies did not show up in higher level assemblies by default.
In "later versions, such as NX12" , display changes applied in subassemblies will show up in higher level assemblies, - depending on how and when the changes where applied.
If the changes where applied before adding it as component to the higher level assy, the translucency will appear by default.
If the changes to translucency where applied after the component had been added, you probably need to "synchronize subassembly properties" to see these in the higher level assy.
i.e
assy_B
|
-Assy_A ( translucency added here)
|-detail_1
|-detail_2
Try RMB- properties on the assy_A in the Assy_B, "synchronize subassembly properties", then the translucency should show up.
Regards,
Tomas