Ian,
To be honest, I'm not sure why watermelon red is so effective. Everything eats them! Bream in particular. Bloodworm and motor oil are also great colours. If your having trouble converting hits into fish, slow down your retrieve a little. This should help a but. Fish them on 1/12 jig heads with size 1 or 2 hook.
Keep at them because they are rapidly becoming one of the best bream plastics around!
Cheers, Tom