“Why is the contrail so black?”
Could be the light, or it could be a military (or crappy civilian — e.g., some Russian POS) aircraft.
I could distinguish F4s from their nasty black contrails all day long.
Heck it could be an ancient Boeing 707 on a cargo flight.
Here:
https://www.metabunk.org/explained-dark-contrails-behind-bright-planes.t5957/
Thanks for the link.