Define RB_SET_PARENT to do all assignments to rb parent pointers. Define RB_SWAP_CHILD to replace the child of a parent with its twin, and use it in 4 places, including rbtree.h. Use RB_SET in rb_link_node to remove the only linuxkpi reference to color, and then drop color- and parent-related definitions that are defined and used only in rbtree.h.
This is intended to be entirely cosmetic, with no impact on program behavior.