Minimal black clothing
Members of the royal family should avoid wearing black during the day. No member of the royal family is expected to wear black unless for a mourning event. It is a rule that had been laid out since decades, however, modern royals, such as Meghan, seem to have broken this rule more than once. For Kate, black should only be worn during mourning and occasionally for nightly events, but she always has some in her suitcase. She seems to be sticking to this rule instead of breaking it. We appreciate that she holds on to the rules more sincerely.
To anticipate a funeral, members of the royal family traveling to another country must pack a set of black clothing in their suitcase. Then, if a family member dies, they have the chance to land in the UK properly dressed. The rule was stipulated because when George VI, the father of Queen Elizabeth II, died she was traveling through Africa, and when she arrived in England she had no black clothes to wear when she got off the plane. It was the day that this rule had been set in place, to avoid any such moments that Queen Elizabeth II had had to go through. In case a member of the royal family is out of country, and a family member at the palace dies, so the returning royal family member will be prepared to dress appropriately.