White growing up I was told it was rude to write letters or notes in red pen.
Unfortunately, no one else seems to have been given this information, and I receive notes written in red ink from others.
All business correspondence should be in black ink, although blue ink is also acceptable.
For casual correspondence, sometimes people like to write using colorful inks for fun. However, in some cultures, red ink is considered one color to avoid when writing or signing one's name because it has a negative connotation and suggests that the writer will die soon.
For more information, see Kammeyer, M. "The Other Customs Barrier: Cultural Research Avoids Business Blunders," Office of Pubic Affairs. United States Department of Commerce. April 2001 www.commerce.gov