What reasons does Crooks first give for not welcoming Lennie into his room in Of Mice and Men?

Crooks is the black stable buck in John Steinbeck's novella Of Mice and Men. Because he is a black man living on an all white ranch in the 1930's he is a victim of both racism and segregation. He is rarely welcomed into the bunkhouse where the white workers live. Candy describes one time when Crooks was invited into the bunkhouse and, because of his color, is involved in a fight. Candy says in chapter two,

"They let the nigger come in that night. Little skinner name of Smitty took after the nigger. Done pretty good, too. The guys wouldn’t let him use his feet, so the nigger got him. If he coulda used his feet, Smitty says he woulda killed the nigger. The guys said on account of the nigger’s got a crooked back, Smitty can’t use his feet.”

Crooks lives in a private room in the barn and when Lennie, who is lonely because George has gone into town, tries to enter, the black man becomes defensive. He tells Lennie that it is not fair for the big man to come into his room because he is not welcomed in the bunkhouse where Lennie lives. When Lennie asks why he is not wanted Crooks says,

“’Cause I’m black. They play cards in there, but I can’t play because I’m black. They say I stink. Well, I tell you, you all of you stink to me.” 

Lennie, of course, doesn't really understand this. He has no awareness of racism. For Lennie, Crooks is just another man on the ranch. He sees Crooks's light and wants the companionship. He doesn't know it's bad to socialize with a black man.