Anecdotes are awesome. But the color of the output depends on the input (kinda for everything I guess?); Temperature, amount of bone, etc.

My understanding is that this is a choice made by funeral homes to provide something “identifiable” to families. They run the furnaces at a lower temperature so that combustion is incomplete. Otherwise you are left with nothing but powdery ash, and people complaining that they can’t tell if the powder really is their loved one’s or not.