Blender to Unity: Surface shading issue with bones

Greetings. This will be my first questions on these forums. I'm working on an independent school project where one of the aims is to model everything in blender and use the built in FBX exporter in Unity (right?) to import the .blend files natively.

Currently I'm trying to create a simple character model and rig it using an armature. The mesh I'm using is made up of several sub meshes for each individual body part. With every bone in the armature connected to a single part. And in Unity, using the provided toon shader.

So far it's been going rather smoothly, aside from one strange anomaly. The lower arms and hands, when attached to their bones, result in the following:

The arm objects become discolored with the toon shading outline color. At first glance it looks as if the normals in the lower arm are flipped, if inspected with diffuse color enabled. But when inspected in blender on the individual parts, they seem consistent.

Again, this happens solely on the lower arms. The bones connect just fine to every other body part and the shading looks normal.

The most recent experiment I conducted trying to analyse the problem was to copy the character's legs, and attach the copies to the bones in the arm. The result of which was no anomaly. The leg copies would connect just fine.

Leading me to believe that some settings with the arm objects are screwed up to a point that it causes anomalies in the model import.

I apologize if this all seems vague but I feel as if my knowledge of Blender has run its course at this point. My last resort would be to recreate the arms. But given that I'm happy with the current form, It would be a shame to start from scratch.

Please, let me know if some part requires further elaboration and I'll do my best to provide.