If you have a white e-caller and you want to use it for calling predators I would either paint it camo or put camo tape over most of the white unless there is snow on the ground.
From what I have seen, if a coyote can clearly see your e-caller there is a good chance the coyote will stop to look at the e-caller that it knows the sound is coming out of.
There is a much better chance of a coyote running right up to a e-caller that blends in or is hidden in grass or rocks.
If you want coyotes to get real close to the e-caller in easy shotgun range, it will happen more often if your e-caller is not easy to see.
If you are shooting a rifle and don't want the coyotes to come into real close range it will happen more often if you put your e-caller in plain sight where the coyotes can see it from a long ways off.