1:72 F18

From what I have seen the plane is all one color. Usually a dull grey. But then add the weathering, and the plane has a black "tint" to it. If you want, I 'll go take some pics of an F-18 for ya. Perks of being military brat and having a Marine Air Base in you "backyard"

Whaz up nsclcctl,
The F-18 was done in a two tone scheme. The over all color is Lt Ghost(compass)Gray FS#36375 w/ the upper surfaces being Dk Ghost(compass)Gray FS 36320.
If you can get a hold of the "Walk Around" book on the 18 by Squadron Signal No.18, you can see in certain pics the tone differences.
I also have a quite a few F-18 pics that I have taken myself and out of all of them 45%(give or take) you can see a diff in the grays(especially on the Canadian variants CF-188's. Its more of a overall Lt Ghost Gray w/ upper surfaces being a med gray)
As ropie mentioned, at times the two colors seem to blend in and looks as if it was one color. This is more so when the a/c has a used look to it(weathered,dingy)
I am sure you can go either way on this and you would not be wrong especially being in 1/72nd.
Hope this gives ya a lil light on the subject.
Flaps up,Mike