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:
There are many different ways to settle on a color theme for your wedding. Some brides have known since they were little girls what colors they wanted to use in their wedding. Some grooms have a strong opinion about one color or another. Still, other couples choose seasonal color and some choose colors which will coordinate with their wedding flowers. There is no rule for how to choose a color theme, or how many colors to choose. Extend the color theme to your invitations _ Some people want every part of their wedding to be color coordinated. Others are less sure. For some people, the traditional ivory paper is what they always imagined as part of their wedding day, while others want their invitations to be as unique as their relationship with their future spouse.