It would be cool if we could apply a custom colour to the Null Shaders shader colour, instead of the default red.
I put together some reasons why:
*Custom shader sets that may represent different things, atmosphere, surface shaders, terrain, objects, etc
*Sometimes I have large sets for release that would be horribly obtrusive if inserted on their own, so I put them into a Null Shader to "Package" them. However, for the end-user, it may be easily lost among shaders, while dealing with a lot of internal parameters for control. A a custom colour would help signify to a user, especially a returning user, that there is more going on here than just the + sign, that it's a "special" shader
*An example could be a darker gray resembling an the Object shader colour, and inside, containing many objects and their respective shaders. Saving a lot of screen save on the end-user importing a TGC into their scene, while also keeping it noticeable that this is a in-depth important element added.
Even I forget about imported sets I've done in the past and go "Wait how do I change these! It's not changing!" than remember it's one of the many internal node networks of one of the many shader sets I have. :P
And after all, the Null Shader is null until given a use, which could represent different things other than the normal red shaders as well as many combinations therein. I think of it like a container. xD
Edit: Additional reason could be many sets organizing shader trees with a simple Legend in a comment box for colour codes, if even needed as the colours themselves could easily help distinguish for the creator.