1. Its tier 3 (Nano), wich is mostly carbon and Energy Crystals
2. The Texture is very blackish.
Correction of 1: Well Carbone and Advanced Alloy have the same tier since they are required at the same time (Adv machines), so that makes no sence. Correction of 2: What if a Texturepack make it greyish when the recipe require carbon? Then you have the same reasons for the other side.
Composite plating makes more sense on the basis of the fact that it is a high operating temperature, designed to accelerate bursts of radiation through a crystalline redstone medium. Carbon nanotubes are a lot lighter and rather tough, and in the world of ic2 a very good conductor of energy shields, however, carbon based materials for the most part are notoriously bad for containing mining level heat dissipation. It's a similar reason to why none of the reactor components are carbon plate, that i'm aware of at least.