This video cites a few interviews where Toriyama admits he's inconsistent with coloring certain characters as he goes with (paraphrased) whatever feels right at the time, or "It's more or less this color". That and it shows actual manga pages and promotional images where Trunks's hair fluctuated between blue or purple. So effectively, Trunks's hair is blue just because.
And one
more thing that's bothered me about this saga, well, all the way back from the first Future Trunks arc, is why Goku and the others couldn't use King Kai to communicate from Otherworld. The anime showed these things are true:
Goku keeps his body in Otherworld, as do Piccolo, Chiaotzu, etc.
Goku died before the Androids showed up, but the rest died
because of the Androids.
King Kai speaks to people telepathically, and Goku occasionally gets to use that for the benefit of his friends. King Kai even allows Mr. Satan to communicate to all of Earth through his telepathy.
Bulma was aware of the existence of New Namek, because the earthlings wished for it in the first place and teleported the Namekians there.
Goku asked about New Namek's location in the Main Timeline, King Kai pointed him in its general direction, and then Goku tried locating the energies of the Namekians to IT there.
The Buu Saga shows that dead people can come back to Earth for one day.
Did the rules of the afterlife change that drastically between one timeline and another? Because with that set-up, Goku could
A) use King Kai to talk to Bulma and the others, and let them know what's up, otherwise KK could talk to them independently and do the same
B) cash in that one-day allowance that he got during the Buu Saga, except earlier, to drop back down to Earth and wipe the floor with the Androids. It's not like he wouldn't be training to get stronger even after he died, and none of the events happened that would lead him to reason that the world doesn't need his help. The fact that he died, and almost everyone he knew followed after him wouldn't lead him to that conclusion.
C) If that doesn't work, then both Goku
and Vegeta could be revived for a day, assuming Vegeta didn't end up in Hell for some reason. They would've no doubt spent a significant time training with each other for the next decade or so until it was Trunks and Gohan's turn to fight.
D) Assuming Goku somehow
is still running on "the world is in more trouble when I'm around, so I'll stay dead" even though the circumstances are different (and technically speaking he was only responsible for Raditz on account of being born), Goku uses his one-day allowance to visit the Namekians and have them revive most characters except him,
especially after the struggle is over, the Androids are finally defeated and there is some level of peace and humanity needs to be rebuilt. Or even
E) Contact Baba and have her locate Dr. Gero's lab with the shutdown remote blueprints, Future Trunks and Gohan would find the blueprints and take them back home, Bulma could then use the schematics to make a remote, and turn the Androids off. That doesn't deal with Cell, but assuming the lab looks exactly the same, Trunks and Gohan could just stumble on it and kill Cell before he's born, with a Ki blast.