Add an emission parameter to the solid color material

[emackey]

Is this worth doing? Basically our default solid color can become complete black depending on lighting conditions, and this introduces an emission percentage that acts as ambient light, preserving visibility of the color.

This does add some complexity to our simplest material, and only fixes the one material. The GridMaterial has a similar fix hard-coded into it. Is there some better way to fix it for all materials?

If we do decide to accept this, we should add CZML & DynamicScene support for the new parameter before this gets merged.

[pjcozzi]

We are several months out from doing a nice lighting system, so we'll welcome incremental improvements in the meantime.

This could be OK, but let @bagnell investigate #924 first.

[mramato]

I think the correct answer here is that we need to fix lighting for 2D and Columbus View (#592) and find the actual cause of #924. Perhaps an ambient lighting setting in the scene would be nice, but I'm not sure we need something per material. It seems like the wrong kind of "fix" (from an API abstraction standpoint).

[emackey]

Rather than adding this to the solid color material, I'm thinking now about what @mramato said above about the desire for a scene-level ambient light setting. We could add something that would affect the outcome of czm_phong and friends to prevent it getting "too dark" (per user setting). In the meantime I'm closing this.