Your examples are good ones. Crooks is discriminated against and kept separate (in part) from the other men on the ranch due to the color of his skin.
Crooks is excluded from the rest of the ranch hands...
Crooks is made to sleep alone, away from the other men who sleep together in the bunk house.
Crooks is also threatened by Curley's wife. She is nearly at the bottom of the social ladder in the situation of the ranch, yet she still has power over Crooks. She threatens him with this power - another example of discrimination based only on skin color.
It is worth pointing out that Curley's wife is also discriminated against (due to her gender). Candy is an outsider and Lennie is too. This group of relatively powerless people are cast together in the story, dreaming together of a better life where friendships, material success, and self-determination are all possible.
As isolated people, even outcasts, Crooks, Lennie, Candy and Curley's wife share a particular, dim hope, articulated by Lennie early in the novel.
"We got a future. We got somebody to talk to that gives a damn about us."
Though Crooks is discriminated against for different reasons than the others, his isolation is ultimately very similar as well as his humble hope. He simply wants to be accepted.