Josh,
I had the same thing happen... dark textures. It may not be the anti virus. This is how I fixed it. First, Check the texture.cfg in the texture folder. I discovered that it was blank. If it is, copy the texture from the another similar aircraft and paste in the texture.cfg of the aircraft you are trying to install. For some reason a lot, not all, of the aircraft texture.cfg's are blank when you download them. Below is an example of what to look for.

[fltsim]
fallback.1=..\..\CS_B757-300-III_PW2043\texture.CS.2018            //CS 300 general
fallback.2=..\..\CS_B757-200-III_RB535E4\texture.CS.2018      //RR CS      
fallback.3=..\..\CS_B757-300-III_PW2043\texture                  //300 general
fallback.4=..\..\CS_B757-200-III_PW2037\texture.CS.2018            //CS general
fallback.5=..\..\CS_B757-200-III_PW2037\texture                  //general
fallback.6=..\..\..\..\Scenery\Global\texture