"Wearing black as a guest at a wedding was considered an insult to the couple getting married? I told me yes. "
Yes, no problem when the guests wear black to a wedding. Nowadays plays a bigger role cutting and the material from which is made the dress with whether suits in space and time is marriage. What you can not have a black dress at the wedding is an idea of mourning. If you are unsure or comfortable with the idea, just choose something else. In my experience, most guests will not choose black as their first choice because of this obsession of mourning. However, it is not wrong if the perfect dress happen to be black. Remember that you can decorate it with colorful accessories.
The couple married is another important indicator. If the bride and groom are very traditional, it can be embarrassing for them to see you wear black on the day of their marriage. The kind of reception can also help you decide if it fits the black. For example, a wedding a sunny afternoon outdoors. The black can not be my first choice. However, once wore a black cocktail dress wedding. The wedding was late afternoon and the couple were a bit elder. I was the only one wearing black that night.
Finally, as a bride and groom, if any of your guests wear black, do not take it as an insult. I am sure that your guest does not mean anything with it unless you are dressed as Queen Victoria in the last years. "