Not sure there is very much more to say about the red dress, that hasn’t been covered extensively.
Mood boards and various notes, below…

Dior
Interesting re invention of a classic Dior from the late 40s. The New Look has been reinterpreted so many, many times.
I was so worried that because Cait is so very fair, that she would be overpowered by brilliant red. It is neither an easy color to use onscreen, but it can eat up a mere mortal. The color made Cait glow like some sort of natural candle flame.
Extraordinary. The dress will NEVER look as good on a mannequin as it does on this particular living, breathing, being.
A quote from Cait-
“It’s a beautiful dress and such a fan moment in the books. Jamie has to say, ‘You can see all the way down to your third rib,’ and it had to fulfill all these different things, so Terry did such an incredible job with it. But walking anywhere, I had to do this kind of sideways crab walk. It was like, ‘Wide load, coming through!’ I thought all that I was missing was the, ‘Beep! Beep! Beep!’ that these massive trucks had.”
One of Balfe’s favorite additions that the writers made is the fact that Claire helps design the dress herself.
“It was nice to be able to see Claire explore her femininity, because she’s usually such a practical and pragmatic person, and not at all interested in her appearance. Being able to see her dressing up for the first time ever, that was a nice element.”
( Fifteen yards of Duchesse Satin)
When trying to figure how to address the notes from the book, I came across this painting.
It gave me the idea that if Claire took a traditional bodice, such as this-
took the embellishment off, and then she opened up the front seam, she would end up with this –
I think it worked for the story and paid homage to the book and the fans of the book/
One last thing- I insisted that we make this. So my amazing team did. They are, once again, the best.
There you go