It's the side you fill out when you send something, also called the list.

Yellow: the second copy, sending the company stub.

This is the side that you are asked to sign when you receive something. SF will take it back after signing. This is called a receipt.

Dark red: the third, the receipt stub.

This was given to you by SF when you received it, and after you signed it.

Green: quadruple, sender's stub.

This is what SF pulled down for you when you filled out the form when you sent something, as proof of your mailing. -Supplement-If the color of the first copy is concerned, blue is an international waybill and red is a domestic waybill.