There have been many different types of rudders. Here are the major ones from the USA:
Fiberglass (Hobie and Third Party):
Fiberglass Race Rudder (Hobie)
Super Rudder (3rd Party)
EPO2 (Carbon, Kevlar and White)
EPO3 (White with Carbon trailing edge)
The Hobie 20 Miracle Rudder
Hobie 21SE Rudder
There are at least 11 different types of rudders:
When Hobie 16s were introduced, they used the ABS plastic rudders that were on the 14s. These had a bad tendency to break off right below the rudder casting. They're a yellowish white, and yellow badly in the sun.
As a consequence, a booming aftermarket developed in polyester/fiberglass rudders. These were often made in a variety of colors and were fairly heavy.
Hobie Cat changed the 16s rudders to injection molded Lexan in the mid/late '70s. Flexible and heavy. They have a waxy appearance, are whiter than the ABS rudders, but also yellow in the sun.
Hobie Cat introduced the EPO rudder in 1983. Black, epoxy foam core fiberglass. Thicker than the older rudders and very light. The only drawback was they hummed badly out of the box. With proper trailing edge treatment to eliminate the humming, these are still the ultimate Hobie rudder. Left in the sun, the outer coating deteriorates, allowing the glass fibers to show.
When Coleman sold Hobie Cat in late 1988, Hobie Cat lost the capability to make EPOs. They came out with black plastic (PCG) rudders and both black and white fiberglass "Racing Rudders" (this is probably what you have).
The PCG rudders were replaced with white nylon rudders in the mid-90's (white, similar characteristics of the Lexan rudders of the late '70s).
In ~2003, Hobie Cat Europe started making carbon fiber rudders. Easily identified by the gray "Hobie Cat" and flying H logo on each side.
In ~2004, Hobie Cat introduced the EPO2 rudder - same shape as the original (with the trailing edge problems fixed). These came in 3 versions - white, carbon fiber and carbon/Kevlar. The carbon/Kevlar version has been discontinued. Easily ID'd by the "EPO2" logo.
Some Brazilians made their own rudders from wood - they were beautiful, but probably not technically superior, especially when compared to the EPOs.