Thought I would mention Guix. I don’t know about using it as an OS but just the package manager is so nice to build reproducible software environments (although disclaimer I discovered this myself a few weeks ago). At least as close you can get without including proprietary hardware drivers. Building MPI applications on my laptop and moving them to an HPC cluster with full performance feels like magic.

The sun’s spectrum at the earth surface peaks in the green color range, which should make green the most efficient choice. Although, I wonder why they have to absorb only a single or a narrow band of color.