They all wore the same, or similar, colours to a public event in show of solidarity behind a specific political and social idea.
Remember, ladies, if you decide to wear one colour to an event - for example, black or dark tones for public vigils and other solemn ceremonies; pastels among the women at weddings; green for the celebrants of St. Patrick's Day - you're actually starting a religion and that religion is a big, scary CULT!!! BOO!
Projection among the Trumpists has become a fucking art form. (And hay, if they can add "ist" to the members of any loosely associated group in existence, even if that "existence" is solely in the head of one deranged rightist, then fuck it; I can, too.)
To some of these people, Trump is not merely a POTUS but also - because God's standards were clearly set aside in this case - an angel on earth. Touching - so touching, in fact, that it's practically groping.
To recap, at least one person thinks liberal women who wore white to a Trump speech as part of their dastardly plan to show solidarity on a very specific and named issue.