I am new to repainting in X-Plane, but have been repainting in the FS series for years. With many FS and P3d paints, you have a .SPEC file that allows you to apply specular effects. These are very common with many of the Carenado variants. Now, I am trying to do a paint in XP-11 that would, if I was in FS/P3d, use the .spec files for a specific highlight color. How are these effects handled in XP with the .PNG files?

There are no specular-files in XP
We have a diffuse file wich holds the "texture" of the plane. PBG or DDS without alpha.
 

Besides that we have normal files ( aka bumpmaps in FSX ) PNG with alpha.
PBR effects ( gloss/materials)  are regulated by this normal-file.
 

See the FAQ for a bit more information about normals and how they work.

 

 

Thank you. I read the FAQ last night, but it didn't mention .SPEC  type files specifically. I suspected that the effect would need to be accomplished through the "Normals", but I wasn't certain. I read how the Normals can be used to simulate polished metal, but can you produce the same type of color highlights in XP-11 using Normals as you can in the FS series through the use of a .spec file?

The answer is a simple NO.
BUT , the Physically-Based Rendering XP11 uses in combination with its real-time-reflectiveness give great ( possibly beter) results anyways.
The only file on wich we can work with colors is the diffuse.png.
In the normal and its alpha-channel we can control how the surface behaves and we can influence colors by the level of reflectiveness to a certain level.

As said ,there is noting alike a specular-file as we know from FSX etc.

You write : Normals can be used to simulate polished metal.

When normals are made the correct way and the OBJ-files for the plane are enabling metalness, we should not say that polished metal is simulated.
The skin of the plane IS real polished metal and mirroring as in real life.
Its not a simulation of reflectiveness, its real reflection/mirroring.