Black ink is necessary for any document intended to be archived on microfiche. Official documents, government forms and business agreements have to be filled out with black ink for the microfilm camera to replicate a legible result.
Forms signed with black ink provide the clearest printed copy. While current technology offers the ability to scan and digitize color, black ink remains the standard to use for signatures.
To distinguish between an original document and a copy, many legal forms now require signatures to be completed with a blue pen. Always read the instructions before filling out any form to remain in compliance.