Sign the letter in blue ink, not black ink. Blue printer: One of the four printing plates in a subtractive colour process which is to be printed in cyan ink. 用蓝墨水而不是用黑墨水签名,因为蓝墨水很容易地让人区别出哪个是正本,哪个是影印副本。蓝版:减色彩印法的四张印版之一。它需用青蓝色墨印刷。
Blue printer: One of the four printing plates in a subtractive colour process which is to be printed in cyan ink. 蓝版:减色彩印法的四张印版之一。它需用青蓝色墨印刷。