There are three colors of Hail Mary flight suits: Yellow, Red, and White.
Yellow is the color of Free Will, or Choice.
Grace regularly wears a yellow rain coat during his time on Earth. When he first arrives on the aircraft carrier, Stratt takes the rain coat away from him and hands it off to another person. Grace does not know it, but his free will has been taken from him the moment he set foot there.
When the astrophage accident occurs, everyone else running towards the exploded building is wearing dark, unremarkable colors that match the dreary day. Grace’s yellow coat shines as the focal point of the shot, emphasizing the weight of the decision he must soon make.
He is wearing this coat when he refuses to join the mission in Stratt's office. The sound design cranks up the crinkle of his movement in it; you can hear the fabric while he is being chased down and pinned to the ground. The rain coat is not included in his belongings aboard the Hail Mary. His free will has been taken from him, and replaced with a false choice: a yellow flight suit with his name on it.
When Grace decides to rouse himself from his post-coma wallowing, he dresses himself and his deceased crew mates in their yellow flight suits. He pledges to Yao and Ilyukhina that he will do his best to carry out the Hail Mary's mission. With no other memory to suggest otherwise, he believes he must have chosen to join as well.
Red is the color of Predestination, or Fate. The existence of the Petrova line establishes this as a very literal Red String of Fate, but this is also carried into the striking red color of the EVA suit. Grace is wearing this color when he makes first contact with Rocky; it is fate that they end up at the same star at the same time. He is wearing the red flight suit while he and Rocky learn how to communicate. Again, their relationship and connection is a product of fate.
Later, when Grace returns to save Rocky, he loosens out all the EVA tether he can and lets it float behind him in the airlock. The Red String of Fate has transitioned for him from solving the Petrova Line Problem to saving Rocky.
White is the color of Sacrifice. Before Grace sends the Beetles off, he records one last video message, and specifically addresses Stratt, telling her that she was right to do what she did. In this message, he is wearing the white flight suit. He has fully accepted his role as a sacrifice, not only for the sake of Earth, but for Erid as well.
Stratt also wears a white sweater when she forces Grace into the Hail Mary mission. She is making a sacrifice as well; she will have to live with this for the rest of her life. In the final flashback sequence where Grace remembers his time on earth in his dreams (while Gracias A La Vida plays), the last shot before he wakes up is of him sedated and about to be placed in the coma. In the background behind his head, we can see Stratt sitting by him, wearing the white sweater with her hands in her lap, rocking back and forth for a couple seconds. Her body language communicates her grief.
Grace's white fox sweater is the ultimate piece to communicate his character arc. Its base color is white, marking him as a sacrifice from the start. The foxes are red, he is hunted by fate. And it is devoid of yellow, showing that he never had any choice in the matter.
