For the record: Yellow and red are both geared the same. They have a low underdrive gear and a standard 1:1 gear. The difference between the red and the yellow is the brake system. The red uses brake discs, these are often found in an advanced state of wear, and are somewhat difficult to find. The yellow uses brake shoes similar to (but not compatible with) those in other Bendix brakes and are much more durable, but the brake side expander cone on the yellow tends to wear out where the bearings run on it, and this piece is very difficult to find.
If you find a low-miles version of either hub and overhaul it properly, it's pretty much a toss-up.
And red was early 1960s, yellow was late 1960s. I have the cut-off year in the book, but I'm not going to look it up right now.
Cheers, Geoff