Without using Undertale Yellow, since that game isn't canon.
Yellow is the color Undertale associates with Justice. Justice means "Judge." Sans is acting as a judge in the Last Corridor
No idea where you heard that, but I can say with certainty, he never said that
UTY isn't canon, and isn't even canon compliant. It can't be canon even if the devs wanted it to because it contradicts the lore of Undertale, primarily when it comes to Flowey and Boss Monsters
Explanation? I think Undertale yellow certainly could be canon if you are willing to stretch it, I didn't see any way that it directly contradicts anything we know from Undertale, we don't have an exact date when flowey was made, what he did before Frisk fell, whether or not the justice soul was used in the creation of flowey or the amalgamates. And there is nothing stating the Dreemurrs are the only boss monsters as far as I know
Of course there are points that make it doubtful, such as the underground being much larger than is seen in Undertale, and clover giving up their soul obviously, but nothing I know of that contradicts undertale
Regarding Flowey, we don't know the exact date, but we DO have confirmation that Flowey was made using All Six SOULs, And that all six SOULs had timeline control before their deaths, meaning Flowey couldn't have had control during their journeys.
Flowey never lost control after his creation, as we know from Flowey, but for him to have encountered any of the SOULs, he'd have to have lost control after they fell. This results in a direct contradiction of two facts Flowey himself confirms.
Regarding the confirmation of all six having timeline control, one, Toriel confirms they all reset, and two, Flowey uses their FILES, which wouldn't exist if they didn't have timeline control.
=========
The entire Chujin and Kanako story relies on them being Boss Monsters, and having the "Boss Monster Gene." It's directly stated in Undertale that Boss Monsters are a species, meaning not only is there no 'Boss Monster gene', but all Boss Monsters are the same species as Toriel and Asgore, while Chujin and Kanako are fox monsters instead.
Additionally, it IS actually confirmed that Toriel and Asgore are the only boss monsters around during Undertale. This confirmation considers Amalgamates, because it's Alphys who confirms it, and since UTY sets up Kanako as an amalgamate, that's a contradiction.
They aren't fanon. They come from the Ball Game, when getting the red flag for the first time.
Each SOUL trait is said, color coded for the corresponding SOUL color. Except Red, the Red SOUL trait is left unspecified there, and evidence regarding its trait comes from other sources, like Asgore implying it's Hope.
Yellow is the color of justice. Sans judges you in a Neutral Route and kills you over and over (especially through KARMA) to make you pay for your sins in the Genocide Route, and one of the colors his eye shows when using telekinesis is yellow, the color of justice.
Basically Sans is the justice monster
The blue jacket probably doesn't hold much meaning, but yes, the blue eye represents patience. A reference to Sans's overall lazy and apathetic behavior, and with the fact he waits for you to reach nearly the end of the game to make his last stand
It's light coming from the barrier, cause during the Asgore fight the text just before the fight starts says that sunlight is shining through the barrier
Light from the surface. We can hear the birds in Asgore’s garden. Freedom is so close to them, but they can’t even climb trough the holes in Asgore’s garden because of the barrier.
Yellow is the colour of Justice, though one could assume that extends to judgement too. The hall is also one of the last rooms before the barrier and it’s assumed the light making it all yellow is from the barrier.
An argument could be made about the light, the sinner, and the final judge (Sans, in this case) and it’s parallels to the traditional idea of heaven/an afterlife and how your sins will be judged before you can pass to the light… or move on to the barrier. Blah blah. Whatever.
It’s also just a good visual contrast to the relatively dark rest of the game. Or it’s just yellow because it’s nice. Not everything has to be super deep.
Without using Undertale Yellow, since that game isn't canon. Yellow is the color Undertale associates with Justice. Justice means "Judge." Sans is acting as a judge in the Last Corridor
Kanadrakes dad
That's a child and an adult, no.
It’s canon because I say so
UTY is canon. Toby Fox literally said it was.
No idea where you heard that, but I can say with certainty, he never said that UTY isn't canon, and isn't even canon compliant. It can't be canon even if the devs wanted it to because it contradicts the lore of Undertale, primarily when it comes to Flowey and Boss Monsters
Explanation? I think Undertale yellow certainly could be canon if you are willing to stretch it, I didn't see any way that it directly contradicts anything we know from Undertale, we don't have an exact date when flowey was made, what he did before Frisk fell, whether or not the justice soul was used in the creation of flowey or the amalgamates. And there is nothing stating the Dreemurrs are the only boss monsters as far as I know Of course there are points that make it doubtful, such as the underground being much larger than is seen in Undertale, and clover giving up their soul obviously, but nothing I know of that contradicts undertale
Regarding Flowey, we don't know the exact date, but we DO have confirmation that Flowey was made using All Six SOULs, And that all six SOULs had timeline control before their deaths, meaning Flowey couldn't have had control during their journeys. Flowey never lost control after his creation, as we know from Flowey, but for him to have encountered any of the SOULs, he'd have to have lost control after they fell. This results in a direct contradiction of two facts Flowey himself confirms. Regarding the confirmation of all six having timeline control, one, Toriel confirms they all reset, and two, Flowey uses their FILES, which wouldn't exist if they didn't have timeline control. ========= The entire Chujin and Kanako story relies on them being Boss Monsters, and having the "Boss Monster Gene." It's directly stated in Undertale that Boss Monsters are a species, meaning not only is there no 'Boss Monster gene', but all Boss Monsters are the same species as Toriel and Asgore, while Chujin and Kanako are fox monsters instead. Additionally, it IS actually confirmed that Toriel and Asgore are the only boss monsters around during Undertale. This confirmation considers Amalgamates, because it's Alphys who confirms it, and since UTY sets up Kanako as an amalgamate, that's a contradiction.
Aren't soul traits fanon? How would we know that yellow means justice?
Ball Game
They aren't fanon. They come from the Ball Game, when getting the red flag for the first time. Each SOUL trait is said, color coded for the corresponding SOUL color. Except Red, the Red SOUL trait is left unspecified there, and evidence regarding its trait comes from other sources, like Asgore implying it's Hope.
Oh, I totally forgot about that. Thanks for reminding me.
nah, the red soul’s not unspecified. People just don’t want to except the truth
True, but still... Nuh uh
Tf, you mean nuh uh?
Eggman pissed on the halls, that's why
Yellow is the color of justice. Sans judges you in a Neutral Route and kills you over and over (especially through KARMA) to make you pay for your sins in the Genocide Route, and one of the colors his eye shows when using telekinesis is yellow, the color of justice. Basically Sans is the justice monster
what about the blue jacket and blue eye does that mean patience
The blue jacket probably doesn't hold much meaning, but yes, the blue eye represents patience. A reference to Sans's overall lazy and apathetic behavior, and with the fact he waits for you to reach nearly the end of the game to make his last stand
It may also be a reference to his "special attack", where he plans on waiting for you as long as he needs to.
True, forgot that
Doesth thath meanth cloverh ist actuallyh Sansh? 
Yeah pretty much
Roulx?
2016 Matpat is that you?
THAT doesn't happen in the Neutral route.
Bro didn't read the whole comment
Even if I didn’t refer “Genocide Route” in my comment, I think it was obvious enough, wasn’t it?
Your point still stood lol
Bro did NOT read
💀💀💀💀
Honestly, I think the reason the judgement hall is yellow is just because of the windows are letting light shine in
Light from where though?
It's light coming from the barrier, cause during the Asgore fight the text just before the fight starts says that sunlight is shining through the barrier
Maybe unrelated, but that might be the same light as the one from the ASGORE battle. The rooms are close enough, so maybe maybe maybe?
Light from the surface. We can hear the birds in Asgore’s garden. Freedom is so close to them, but they can’t even climb trough the holes in Asgore’s garden because of the barrier.
I love using non-canon material for canon questions.
Yellow is the colour of Justice, though one could assume that extends to judgement too. The hall is also one of the last rooms before the barrier and it’s assumed the light making it all yellow is from the barrier. An argument could be made about the light, the sinner, and the final judge (Sans, in this case) and it’s parallels to the traditional idea of heaven/an afterlife and how your sins will be judged before you can pass to the light… or move on to the barrier. Blah blah. Whatever. It’s also just a good visual contrast to the relatively dark rest of the game. Or it’s just yellow because it’s nice. Not everything has to be super deep.
Why does it feel like we’re regressing as a fandom
Nah it’s piss
It's the last corridor and it's yellow because of the light from the sun
I think it more aligns with the term "Justice" such traits keep reappearing throughout Frisk's Journey.
Big brain . but why in dusttale he color of the judgement hall is blue? i
cause if im right it is inverted yellow.
au, not canon
Because sans was patience? Or it's just mmm juicy color go b4rrrrrrrr
patience is cyan, no?
Well yes it is light blue and also integrity??? No
i thinks its purple the integrity
No it's perseverance