Combining ideas _ Some couples choose a neutral color for the invitation itself, and compliment it with ink in one of their wedding colors. You can also add a bow to many invitations. If your invitations have a bow, you can choose a color that coordinates with your ink color or matches it. No couple is beholden to extending their wedding color theme into their invitations, many do, but there are many other alternatives.
This will vary a bit depending on whether parents are issuing the invitation or whether the couple are doing so but in general this style is acceptable: