If you are signing any formal paperwork, blue ink is a safe bet. The idea is you want your signature to look different from the rest of the document, and since most papers are printed in black ink, blue will pop and prove that your signature (and the signed document) is legitimate. When it comes to hand-written cards, think thank you notes, invitations or professional notes, black ink is always a safe bet. If you’re a creative type, there are a few instances where colored ink is acceptable.
