Real guns don't have white trades so why put them on an airsoft gun?
When painting its good to wipe down the receiver with rubbing alcohol or something else like that to get rid of all the grease and such. The plastic WILL still be transparent after the first coat, unless you put on too much but then it might run or crack when it drys. The Krylon camo series in the Fusion line is the best as it bonds with plastic chemically. If you aren't disassembling the gun (which isn't required) remember to put something in the hopup mag well hole so no paint gets in the hopup or inner barrel. If painting the front end plug the inner barrel with some paper towel or something.