Personally, I almost always have a darker nail polish (deep purples, reds, blues, etc.) and chose to do a royal-navy blue "cat eye" style manicure for the big day as well as blue toenail polish. If dark fingernails are something you're totally not into, the toes may still be okay? I also had blue panties as I didn't wear a garter but if your dress is too sheer this may also be a no-go.
Other things you could consider are: jewelry with some blue (double points if it's your "borrowed" from a family member!), a blue hairpiece/beret, a blue handkerchief to tuck away for the ceremony, blue ribbon wrapped around your bouquet, or a small blue trim around the bottom of your veil.
My dad gave me a blue sapphire ring for my 12th birthday. He passed when I was 14 and the ring is one of the only things I have to remember him by. It doesn't fit anymore because I'm a grown woman, but I will wear it on my pinky finger as my "something blue" so that he is close to me.