The law does not clearly stipulate whether the IOUs should be printed with handprints or inkpad of what color. The purpose of restraining fingerprints is to identify whether the borrower himself has behavior. In order to avoid disputes, it is best for me to write the contents of the loan on the copy of the other party's ID card (if it is a loan, it should be clearly stated), and I will sign and seal it. As for color, it is common in life and easy to identify.