An old line attributed to automaker Henry Ford goes that customers could have any color they wanted for his Model T, just as long as it was black.
Much of that sentiment can be applied to the color ink you should use for notarizations. Black is the recommended ink color to use when affixing an official Notary signature or seal because it shows up legibly in microfilm or photocopies.
There are a few exceptions. Utah requires purple ink so that a black-and-white photocopied document can be differentiated from the original. Tennessee is the most notable exception; the only colors you can’t use are black or yellow.