Why would your windshield turn green or foggy when it was hit by the air from the blower?

Because the moisture in the air is condensing on the cold glass. Warm air carries more moisture so in the winter if you can turn on your A/C and turn the heat up to hot then the Windows will clear quicker and if you live in a humid or rainy climate turning the air to recirculate (see owners manual) then the air inside the car will dry out quicker and the Windows will stay clear. Also if you get in the car with wet cloths on then that will add moisture into the air in the car. Repeat the steps above and be patient. The green color is just coming from the color of the glass and is nothing to worry about it will clear once the window is dry and warm.