The "glass" texture must be a non-transparent texture itself.
ex.
The "Blank" texture is 100% transparent, and will take in full color when painted.
The "black50" texture is 50% transparent, 50% solid black. will be 50% darker color when painted.
The "black" texture is 0% transparent, and 100% black. Painting will have no effect.
So for the effect you want to get, try using a blue texture that is 0% transparent. If this ends up being TOO blue, then just darken the color until satisfied