Turning white???
The breathing and gaping is a normal moray occurance. However, if he is really looking sickly when doing so, I suggest trying to increase the oxygen in the tank.
In case of emergencies, you could always put a few drops of Hydrogen Peroxide into the tank, it breaks down into O2 and H20 - but don't put too much, could harm live plants. Depends on the tank size.
I would suggest adding an airstone for the long term, to increase oxygen.