Board Thread:General Discussion/@comment-27581425-20170619123421/@comment-36564422-20180812213229

I think that it goes like

Red (Chara) > Yellow > Purple > Cyan > Blue > Green > Orange > Red (Frisk) > Black (Hated by everyone on genocide route) / White (Loved by every monster on pacifist)

My theory is that when Chara died, yellow wanted JUSTICE for Chara, but then they died, so a long time after that, purple PERSEVERED to go on through, but also died, then Cyan heard about it, so they went down there, and was PATIENT through the underground, but they still died, then blue told their parents that they were going to Mt. Ebott, because they had INTEGRITY, but they also died, then green went down there, and they were very KIND to the monsters, but since they were a human, the monsters had to kill the green soul, then orange was BRAVE enough to go down there, even after what they heard, but died as well. And you know the rest, frisk either frees the monsters and is LOVED by all monsters (the good love), or kills all of the monsters and starts killing humans as well, then they were HATED by everyone.

So, there's my theory on which order the souls go in