Why does dry hydrogen gas have no effect on litmus? is it because it's neutral?

Dry hydrogen gas have no effect on litmus because when the gas comes into contact with the water on the paper, it becomes acidic and turns the litmus paper red. 
The main use of litmus is to test whether a solution is acidic or basic.The gases dissolve into the water and the resulting solution makes the litmus paper colored (Color depends upon the gas used).

List the following gasses