I have the Walgreens kit, and what Marc said applies to my kit.
The host fitting has white plastic inside where the contacts are.
The other one, (I call it a sync fitting), is has black plastic inside where the contacts are.
My Palm sync cable, is also black on the inside.
I recived 2 "Host" cables from StreamlineCPUs when I ordered my SL-C3100, and the inside plastic is also white.
The shape also gives them identification, if you look at it under a good light.
Also, it's hard to remember, just by the shape of the plug.
(That pic I attached above is the only pic I had. I don't have a "good" digital camera)
Jon