Starting with the 356A in late 1955, Porsche used a plastic plate to cover the hole in the center of the dash if the new owner did not order a factory radio. Sometimes called "radio delete plates", the A and B parts books list the plates but do not show color options. However, three different colors are known to have been used: black, grey, and beige. The expert consensus seems to be that the beige plates were used on the 356A model to go with the beige knobs. The uncommon grey plates may have been used to go with the rarer grey dash knobs, which are sometimes found on T2 Speedsters. Starting with the 1960 model year, the black plates were used due to the change to black dash knobs in all models of the 356B. The 356C also used the black plates. [Original beige plate shown above right, photo courtesy of Freddy Rabbat]
The original beige plates had gold lettering, as shown in the photo of Freddy Rabbat's original plate (above right and bottom of page). The rarer grey plates probably had gold lettering as well. Based on information from 356C owners Mark Hubbard and Don Sanford, their original black plates came with silver lettering (photo below) and gold lettering, respectively, so perhaps the black plates could have come either way. Brett Johnson states that all the NOS plates purchased by Tweeks from Porsche in the 1970s and early 80s had gold lettering. Regarding the grey plates, Steve Douglas (original 356A coupe owner) thinks it possible that they were only offered on the late A cars with certain color combinations, and believes that some early As may have come with beige plates with silver letters.
Identifying Reproduction Plates
It seems likely that the radio plates used by Porsche during 356A through C production had the lettering embossed into the back of the plate, and that modern reproductions can be identified by their lack of embossed lettering. This may be the easiest way to tell a repro from an original (see photos shown below). In addition, the originals are slightly thicker and have a more rounded edge, while the repros tend to be thinner and have a sharp edge. I have not seen repros with gold lettering (though some 356ers tell me they have), they are usually silver, but I have seen them with uneven bluish lettering as well.
This issue of how to reliably tell a reproduction plate from an original is far from settled. If you have information or photos to contribute, please email me at firstname.lastname@example.org.