Received the following info from Ted Brindle:
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There are three types of fuel pump membranes available. The black one is the rubberized fiber, the Beige one is fiberglass based, and the blue one is Acetate. They all work well, but the black one moves more gas than the others but it wears out the fastest. The Beige one works best if you use methanol fuel and is reasonably durable. The Blue Acetate is the most durable but pumps the least fuel.

http://tech.flygsw.org/walbro_tuneup.htm