One time when trying out a new call for the first time, I called in 4 coyotes at one time to within 80 yds. I was sitting on a bare hillside that wouldn't hide a coffee cup. There were two of us there, we were both wearing blue jeans and flanel shirts and baseball caps.
I believe that you can probably call in predators wearing a Santa Clause Suit.
The important things are keeping your movement down, sitting in the shade if at all possible. At least try to keep the sun behind you (not glaring/shining off your gun,face,fingernails,watch, calls, binos, ect). Having a rock or brush behind you and a little something low and in front of you helps alot to break up any outline they may see too. Sit low enough that you don't appear to be on the skyline to the predator approaching from below you.
Location and how you handle the situation when the coyotes show up will make or break the coyote callers success. Getting within range of coyotes ears without being detected/spotted is more critical than what color or brand of camo you choose. Setting up where the coyotes have to "show" themselves in order to smell or see you is more critical than the brand of call you decide to buy. Handle the situation effectively; remaining calm, patient, stealthy and making every shot count is more critical than the caliber you choose to use.
But none of this means a **** if we're calling in areas where there aren't any coyotes at the time, or if someone else was calling/shooting in the same area very recently, and the coyotes have been educated to avoid the sounds of calls.
Didn't mean to get off the subject of your question, but my point is to pick something you are comfortable in. There is no need to become invisible unless you simply want to, and no ONE camo pattern works everywhere anyway.
Good Luck to you and all in your predator pursuits.