The purple and silver gun looks like an HVLP (High Volume / Low Pressure) sprayer, not an airbrush. That little airbrush compressor probably does not put out enough volume to drive it. (But it may put out enough pressure whent the sprayer trigger is closed that the sprayer vents itself to prevent overpressure. I don't know if your sprayer does that.)
Do you have a regulator? (Is there a knob on the other side of the separator/gauge assembly?)
If you have a regulator that vents downstream pressure, it will "leak" by design until you adjust it up to the right pressure range; after that it will leak extra pressure that accumulates between it and the airbrush. That's a good thing, if I correctly understand how these things are supposed to work.
(My understanding is that most valves leak a tiny bit, so when you're not spraying, air gradually leaks into the hose between your regulator and your sprayer, until the pressure there is equal to the pressure in the tank, rather than the lower pressure it's supposed to be regulated down to. Then when you hit the trigger, you get a brief PFFT! of too much pressure until the pressure is relieved. Venting downstream pressure prevents this accumulation of excess pressure in the hose.)
The bottom line there is that the leakage you hear may be perfectly normal, and your problem may be elsewhere---e.g., not having adjusted your regulator up, or something entirely else.
Does your system have auto on/off, where the compressor kicks on when the pressure in the tank drops to some pressure (say, 50 PSI) and turns off when it hits some higher pressure (say, 80 PSI)? (I'm guessing that's what the black box on top is, but I could be wrong.)
Paul
