“...I wonder why, unlike everyone else, my soul has color... will I ever find out the meaning of this..?”

Sad!Papyrus Triva:

Use of the scarf primary to cover/hide his neck

Magic is a dull orange which gets a little grey in the centre (due major loss of optimism)

He is the only thing that stands between Sans and insanity

Does not want to be in the royal guard anymore

Therefor his new dream is to cheer everyone up again, despite being downright depressed and traumatised himself

Even bigger is his determination to give Sans his will to life back

After Sans stopped doing puns, Papyrus decided to continue on with it, because they make others smile. Started to like them.

Despite not looking like it anymore he probably still is the most optimistic monster left underground Tries to be optimistic, but is terrible at hiding his feelings most of the time. Breaks down only when alone or with Sans around though.

His self esteem got a HUGE crack. Doesn´t refer himself as “the great Papyrus” anymore, but simply with “Papyrus”.

Actually got insecure with pretty much everything and tends to stutter when talking to someone new

After everything Frisk/Chara had put them through, he doubts if there is good in everyone

The crack on his skull comes from the human breaking his head after they cut/ripped it off

Scared of whatever object the human killed him with (Toy Knife and Tough Glove), triggers memories of his murder, instant mental breakdown when in sight

In a world that got destroyed just to be rebuilt again and this over and over and over, it is hard for one to hold onto hope. 

Sans - broken heart - has no hope anymore