The first 2 coats of Klear provide a smooth surface for the decals and protect the paint from the weathering process. The second 2, or more, level out the decals with the surface and protect them. For an aircraft operating in the Pacific theatre (and the Mediterranean/desert too) I like to fade the paint. This can be scary, but the Klear allows you to remove it if it's not successful. This fading needs to be done over everything that would be exposed to the elements. I use enamel medium sea grey, heavily thinned and build it up gradually and randomly. If it is done to evenly the affect is lost and you might just as well have painted it in a lighter colour to begin with. I "attacked" individual panels on the upper wings and top of the fuselage only. Don't forget the tops of the canopies, slats and the dive brakes. When this fading is complete then another coat of Klear is required, to protect the fading.
I then applied a wash. I use white spirit and artists oil paint. I never use straight black-much to harsh. I generally use warm grey-it has a brownish hue, raw umber, or brown madder, darkened with a little black. I leave the wash for several hours. I sometime use a "sludge wash", which is much thicker and leave it on for 24 hours or more. I wipe the excess wash off, in the direction of the airflow. This is so that the wash leaves a slight tint. Using a minute amount of neat oil paint and dragging it back with the finger, a cloth or cotton bud, to represent oil and/or grease marks can enhance this.