Addressing a yellow envelope follows the same general rules as addressing any other envelope. The most important thing is to ensure that the recipient’s address is clearly and correctly written in the center of the envelope, with the return address in the top left corner. When addressing a yellow envelope, you may want to use a contrasting ink color, such as black or blue, to ensure that the address is easy to read. You may also want to use a slightly larger font size than you would on a white envelope, as the yellow color can make it more difficult to read small text.
There is no specific etiquette associated with using a yellow envelope, so you can use it for any type of correspondence. However, yellow envelopes are often used for special occasions, such as weddings, birthdays, or holidays. You may also want to use a yellow envelope if you are sending a particularly important or sensitive document, as the bright color will help it stand out from other mail.