Many courts, as well as other government agencies have expressed their preference that all documents requiring original signatures should be signed in color, rather than in black ink. This is because original signatures in black ink may be mistaken for copies and, as such, can be rejected. This in turn can result in a significant delay, and missing a filing deadline can mean an end to a case.
The advance in technology and vast improvements in photocopiers and scanners mean that the quality of documents produced by printers and copiers makes those documents nearly indistinguishable from the originals. As such, it is easy to see why some officials can confuse an original for a photocopy.
Using blue pen to sign all legal documents is probably the safest way to go, as it is a professional color and frankly, you will not impress the judge if you submit your documents signed in purple, green, or fluorescent pink.