This one is somewhat down to personal preference, though there are some pragmatic considerations to take into account.
If your pen is for business or everyday use, then the choice is narrowed down to blue or black. On balance, though, black edges it on the grounds that it looks more professional and is a legal requirement for signing legal documents and form-filling etc.
Often, the requirement for black ink is because the forms are to be digitally scanned, and scanners, like photocopiers, seem to prefer black ink to blue. Presumably, because black ink on white paper offers the best contrast and therefore increases accuracy.
Red ink, meanwhile, is another option, especially if you have to edit paper documents and print outs on a regular basis. Here, red ink is ideal for highlighting amendments or deletions as it leaps out of the paper more so than black or blue which tend to fade into the surrounding text.
Green ink is not an option, unless you like to write crank letters.
If your pen is for business or everyday use, then the choice is narrowed down to blue or black. On balance, though, black edges it on the grounds that it looks more professional and is a legal requirement for signing legal documents and form-filling etc.
Often, the requirement for black ink is because the forms are to be digitally scanned, and scanners, like photocopiers, seem to prefer black ink to blue. Presumably, because black ink on white paper offers the best contrast and therefore increases accuracy.
Red ink, meanwhile, is another option, especially if you have to edit paper documents and print outs on a regular basis. Here, red ink is ideal for highlighting amendments or deletions as it leaps out of the paper more so than black or blue which tend to fade into the surrounding text.
Green ink is not an option, unless you like to write crank letters.