The parotoid gland is found on the back, neck and shoulders of toads. It secretes a milky alkaloid substance called bufotoxin, to deter predators. Bufotoxin operates as a neurotoxin.
In the picture of an American Toad Anaxyrus americanus americanus below, taken locally in Cambridge, ON, the raised glands are very visible, located somewhat behind the eyes.
American Toads present an entire range of colouration, as can be see from the following pictures, all from an area within a thirty kilometre range from my house. Doubtless the colour of the skin can change hue depending on environmental conditions and the substrate in which the toad finds itself.
In all instances the parotoid glands are clearly visible, although not as prominent as in the first picture, where they are a lighter shade than the rest of the toad's skin.
I have no doubt that the secretion of bufotoxin is effective as an anti-predator strategy in many instances, but as far as I can tell, it appears to offer little defence against avian predators such as Broad-winged Hawk Buteo platypterus or Great Blue Heron Ardea herodias.