I also discovered that there can only be one Determination soul existing at the same time, same with Fear. While it's true that only fear can beat Determination, only Determination can defeat Fear as well.
FEAR is a very powerful inverted trait that is strong enough to defeat any other soul traits (including Determination, even though victory isn't always guaranteed).
It is impossible to naturally be born with a dark orange soul. Instead, someone can turn their soul dark orange by reverting their trait of Bravery to Fear.
In fact, FEAR's natural color is dark orange, but when the Bête Noire spell used on the Fear trait, it is pink. Camila confirmed this information in a tumblr post.
Known Powers and Abilities
Hallucination Manipulation : It appears as though the known wielders of the FEAR trait can create and control hallucinations to strike fear into the hearts of their opponents.
FEAR Weapons : If the user wishes, a soul collector can create a powerful spear which is dark orange in color. FEAR's spear is similar to Bravery's spear.
Feeding on FEAR : Fear traits usually get more stronger when more fear is around so they feed on the fears of others and even their own to get stronger.
Rhabdophobia : This special attack disables all enemies' attacks and attracts magical weapons to the user's side, But it can be very costly to use because it consumes almost all the power of the user. It is a very powerful attack.
Fear of death : This may only apply to Betty as they have this specific phobia, usually when closer to death they get more stronger depending on how close they are to death. This is seen in Do or Die, when Gaster was about to blast his Gaster Blaster to Betty, their hair turned fully pink and with enough strength Akumu escaped the green force field Gaster trapped Akumu in.
HATE is MUCH more powerful than FEAR. However, FEAR is a physical soul trait while HATE isn't.
Only one Fear soul trait can exist at any moment, and the same goes for Determination, and only Fear can defeat Determination and vice versa.
A negative trait like Fear, will give a person more power at the cost of their sanity.
Camila Cuevas said on her Tumblr page that the Bete's soul was pink because pink is a color that usually looks innocent and can also trick the characters and the viewers.
This may only apply to the vessels of "The Bete Noire" spell.
FEAR is not a new soul trait. The Fear trait is just the inverted trait of the Bravery. That's why a Fear user can use the Bravery's weapons, like spears.
Kumu and Betty are just a physical form of a FEAR trait.
Although the FEAR trait is the opposite of the Bravery trait, the Bravery trait can't beat the FEAR trait because Negatives are always strong.
Agate is one of the humans to possess a Fear soul trait.
She wasn't the first one as someone else has done "The Bete Noire" spell before (Which requires a FEAR trait so Agate wasn't the first person to have a Fear soul trait). So Betty isn't the first of her kind.
Camila stated in the comments of Glitchtale Origins "FEAR is just a darker version of orange. Using your soul for the bete noire spell makes it pink".
Fear is the only known negative counterpart of a trait so far.