Sans wears a lightish kind of blue hoodie along with lighter blue shorts. His pupils are also blue. Sometimes he is drawn with a black coat and jeans giving the player a Bad Time.
Toriel - Sans is very kind to Toriel and Toriel is the same way to him. They share soul jokes together through the Ruins exit.
Papyrus - Sans loves trolling his brother sometimes. He is very protective of him and has patience in his ridiculousness.
Sans just acts as his normal self during the Pacifist route, only he talks with his Brother and meets the human after their talk.
San's soul suddenly turns into Justice after witnessing his brother die while waiting for the human. Once he finds the human in Soul Hall, he called them a "Monster", lowering the human's defense just a bit because they get called a monster many times.
"So you made this far and yet you spread the dust of our souls along the way."
"But... I wont let you keep going.'
"I will not serve you the dust of me, but I will serve you JUSTICE"
- Sans is one of the few monsters in Soultale in which his soul changes during a route.