There is a difference between dressing diplomatically in a respectful manner and literally doing a stereotypical cosplay of what you think represents the country you're representing. You want to dress in a way where it's respectful and not veering into costume territory. Kate's outfit today was on the verge of a costume.
What Kate wore today reminds me of the controversial outfits Justin Trudeau wore in India. It's just patronizing and an eyesore. I know she dresses similarly during St. Patrick's Day, but I honestly think that those outfits were way more coherent and understated. The outfits usually fit into the environment and complement those around her.
Today, she's dressed in bright-ass Shamrock in a quasi-military-inspired outfit. It's clear that she really wanted to stand out and call attention to her new position. Not to mention the late Queen also wore a similar shade of green last year. However, it comes at the expense of Kate just looking so gaudy and stereotypical. Her green against everyone else's red makes it look like Christmas. I would have preferred that she just wore the dress in a different colour (black or alter it to a deeper green/blue) and added the Shamrock pin as a nod to her regiment. That way you still get the military look and no Lucky Charms But Make it Fashion.