Colorblind person here. If we’re talking about limited visibility differentiation of front and back, the color of light is way less noticeable than whether we’re looking at headlights or not (based on intensity). There would be no issue telling whether we’re looking at a front brake light or a back brake light so long as the front brake light has headlights around it.

This was my first thought as well. Both sodium hydroxide and sodium bicarbonate seem like they could have a signficant environmental impact. We’d need some good studies on that before committing to this idea, I think.

The technology plans for these fuel cells aren’t “for now”. They’re for a future where we’ve hopefully already decarbonized most of the electric grid, as doing so is way more important than decarbonizing aviation. Converting fleets of airplanes to electric is a long process that will probably not be started for a while yet while there are more important carbon emission sources to tackle (aviation is only 2-3% of the emissions right now).