fashion advice needed for smart London wedding in hotel

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Hi all, I have bought this dress www.johnlewis.com/somerset-by-alice-temperley-cutwork-dress-blue/p370706 for a wedding in April at a 5 star London hotel. Going to wear it with silver stilettos I already have, but what colour cardigan,(rather than jacket as the whole thing is in a nice hotel) ? Neutralish or LK Bennet do a nice berry colour one, was thinking blue maybe a bit boring or something completely different but any ideas? Am splashing out as don't want to look like frumpy 40 something mummy (or too mutton) but also as I wear cardigans a lot will get a lot of use out of it (I hope!). I have medium brown hair, pale skins and grey/blue eyes if that helps at all!

That dress is LOVELY and will compliment your shoe choice perfectly. I can't help feel that a bit of colour would be a nice addition, so I have chosen these to suggest -

This pink peplum cardigan from Monsoon is very sweet, the peplum will suit the slight retro feel of the dress. I am not a fan of bolero styles and a longer one will look a bit every day, but this strikes a nice balance. I think it would look nice with a tea dress too, so easy to wear afterwards.

I really like this lemon yellow cashmere cardigan from John Lewis too. I love the collar style, the yellow is one of the main colours of this season and I can easily imagine it with a white vest, boyfriend jeans and tan sandals in the summer.