My client chose blue for her invitations, kind of apropos to feel the blues as I write them as Summer begins to wane and the Olympics are no longer my background music! 
As you can see she chose the classic outer and inner envelope style. You can find out more about how to address these two envelopes from both Martha Stewart and Crane & Company. As Crane & Co.’s blog explains, long ago, Wedding Invites were delivered by the Bride’s footmen to guests homes. The guests’ servant removed the pristine inner envelope bearing only the guest name from the outer envelope. 
“Though footmen have since been replaced by postmen, the inside envelope is still de rigueur. It gives something as important as your wedding invitation a certain je ne sais quoi.”
Having addressed many envelopes, both formal and informal, I often tell my clients, that this is the first opportunity to present your guests with the ‘style’ of your Wedding, whether formal or casual. If your Wedding is informal, the inner envelope is an opportunity to write your guest’s nickname or the name you’ve come to know and love them as.
