Posted By: 
petecldLeon,
I read the title and started thinking about my best friend's bachleor party and we. . . .uh, never mind.  
When you're talking about hand stamping, I believe the standard ink color for stamp pads was/is purple. That way when you stamp a sheet of paper with black copy on it it wouldn't affect readability.  A black stamp over black text would start to make it hard to read.