I refuse to send out a plain envelope in the mail. It really takes very little effort to fill up an envelope with color. This is my rent check envelope. This is the back of the envelope. Here I used Tombow markers and detailed with a extra fine tip Black Sharpie.
This is the front of the rent check envelope. To say the least, my landlord knows when my rent check arrives and has expressed his appreciation of the extra effort. His office carefully opens the envelope and has collected them over the 10 years that I have been sending them. His secretary teases that she is going to have an exhibition of my rent check envelopes.