Technical old snap on paint gun id

]Any one know what model this snap on gun is, no numbers on it and cant find it online. Also. what does the knurled knob in the middle opening control, i cant get it to move, guess i need to soak the gun to loosen it.

weird not sure where pic went first time but here it is

DSCF1109 by h2omonkey posted Aug 4, 2014 at 6:16 PM

 

Apparently the middle knob is a cloaking device. Turn it the other way so we can see it.

 

Stealth model, rarely seen.

 

Looks easy to clean.

 

I think it's ot a coating of clear on it.
-Pat

 

Is it white?