Here is perhaps the most elusive model for any Zenith collector. It is the see-through version of the maroon handwired Royal 500. It is hard to tell how many of these exist, but the popular thought is that the earliest maroon sets were made out of a slightly different nylon composition that actually allowed you to see through the material under certain conditions. It is best witnessed by removing the back and holding it up to the light. If you remove the chassis, you can do the same to the front. Check the photos below to see what I mean.
A translucent set can have up to 5 parts that are made out of this see-through material: the front, the back, the battery cover, and the two knobs. The battery cover will usually have a black backing under the label to help shield it from showing through from the outside. However, this example does not.
The strange thing about these translucents is that not every example has all of these parts made out of the translucent material. The rarest I have found are the ones that have the see-through knobs (in addition to the other three parts). The one pictured below has all the parts out of the translucent material and is an early serial # of 9,130. The tuning capacitor date is the 46th week of 1955, making it in the early production days when these were first introduced to the public in November, 1955.