According to the requirements of archives, it is best to use black, because it has high carbon content and is suitable for long-term preservation. Why ancient paintings and calligraphy can still be seen for thousands of years is because the ancients used ink, which has a high carbon content. However, although the current files are required to be filled in black, as long as they are not top secret files, blue files can be used. Unless the file teacher is a strict person, you are in big trouble. Fill it out again!