They used chemicals that caused their skin to turn yellow hence the name "canary girls"
yes.
canaries are birds
In breeding some times, for food if there isn't enough sometimes.. though no they usually don't. And if they do the females don't fight back.
If you want to breed a white canary and a yellow, It is possible as long as the type is the same. such as: Specked white Canaries can breed with speckled blue Canaries or even yellow you know.