I was writing a thank-you letter to my grandmother and put together this gray envelope with white calligraphy. Originally, it just had gold/yellow stamps, but I added in some pink and thought about how pretty and feminine a color combination pink and gold is.
L to R: Dahlia from the “Roses” block (all pink Scott 1876-1879); Progress in Electronics (Scott C86); Edgar Allen Poe (Scott 986); Library of Congress (Scott 3390); Connecticut (Scott 772). This envelope is, as I said, a thank-you note, so while I think it could work splendidly for weddings, you could also go with something a little more refined with the color scheme and do gold calligraphy on white with pink stamps or vice-versa, or black calligraphy on a pale pink envelope with gold stamps. A couple more stamps that fall into the color scheme:
L to R: Puerto Rico (Scott 1437); Orchids (from the Orchids block–3 are pink, one is yellow: Scott 2076-2079); Armed Forces Reserve (Scott 1067); 300th Anniversary of New York (Scott 1027). Gold is a bit harder to find (provided you don’t want to use Christmas stamps) than pink–pink you can find almost anywhere, particularly in the older stamps at smaller denominations.
…And my favorite, which I don’t have anymore–Emily Dickinson may have been a 19th-century poet, but this stamp looks so 50s to me–which is sort of the essence of pink and gold: