16th of January, 2009
Generally, blue is best for legal documents, as it contrasts with the black print. That contrast helps distinguish originals from copies (with the caveat that a good color copier may break that rule). Also, blue usually shows as lighter than the original print on a b&w copier, although I can say from experience that Noodler's Luxury Blue copies as black as the original print.
Some states (or local courts) specify what color ink should be used, so you may want to check on that in your area. To add to the confusion, sometimes the same jurisdiction will require different colors on different document types! For instance, the same court may require that briefs be signed in black, motions in blue or black, and real estate documents in blue! And state agencies may have their own separate requirements. (Any local attorney should know which is which.)
I work in a law office, and use Noodler's Luxury Blue for everything, but I also carry a pen in my jacket filled with Noodler's Black for certain documents. (At least one form we use regularly specifies "black, nonfading ink.")
Hope this helps!