I think the black suit was a great idea as it allowed the lovely dresses and suits of the children and their chaperones to shine. Clearly they all went to considerable effort. I think she allowed the children to be the stars.
In the US, black isn't considered funereal (and women wear far less frumpy outfits to weddings, including chic black outfits, than the British UC do).
Bootcuts are on the way back, you say??!! [good, finally, and thanks]