I go 4 fingers down from the collar on the front, and just under the front collar impression on the backside of the shirt. everyones fingers are different so I measured mine and the 4 fingers measure 3.5. I also use my left hand to guage where to put left chest logos.
Grey noise then, has a sound frequency that, if translated to a light frequency, would roughly be the color grey. Grey noise is a random sound that is distinguishable from other types of sound because it sounds the same, to the human ear, at all frequencies.
Pure white/pink/brown noise starts annoying me pretty quickly if it's not broken up at all. If I'm tired, the white noise will put me to sleep right in my chair. In that case, electronic or classical music with minimum vocals works to block out noise and help keep me awake.