Lower parts kit comes is color coded kit for easier assembly of your lower.  Each color code is tied to a area of the lower receiver.

WHITE: Take down pin, Receiver Pivot pin, Take down pin detent (2), Take down pin detent spring.
YELLOW: Bolt Catch, Bolt catch plunger, Bolt catch spring pin, Catch spring pin, Catch spring, Buffer retainer, Buffer retainer Spring.
RED: Hammer & Trigger Pin (2), Hammer Spring, Trigger Spring, Disconnect, Disconnect Spring.
BLUE: Magazine Catch, Magazine Catch Spring, Magazine Release Button, Trigger Guard Assembly, Trigger Guard Pivot Pin Spring.
BLACK: Safety Selector, Selector Detent, Selector Detent Spring, Lock Washer, Pistol Grip Screw.

Hammer, Trigger, Black Pistol Grip.