i was taught to get my clients to hold tennis balls as this helps to stop the palms getting tanned, it really works and always raises a laugh when I ask clients to "hold my balls".
As for not being able to see if the gun is spraying, try spraying 1st on a piece of plain white kitchen roll, make sure you give the solution a good shake 1st. When you tighten the needle at the rear of the gun, get a permanent marker and mark it where it is at the tighest point & then if you turn the screw anti clockwise to somewhere in between 1/4 to & 1/2 past (as in on a clock) then this is roughly a good indicator to the amount of solution you should be using, but it depends on the guide colour of the solution you are using. When you spray onto the kitchen roll it should not be wet through, it should be almost dry, if you still cannot see the guide colour you may need to change solution to one which has a stronger guide colour.
I hope this helps xxx