The soles of my shoes are a light blue; I got lucky with that one. I don’t think it really needs to be shown; at least mine isn’t going to be. I think the easiest/cheapest way is to either have a blue garter or blue undies. Blue is my least favorite color, not really sure why... good luck!
I like all the Pinterest photos that show the bride putting the something blue inside her dress, such as the date stitched into the hem or a piece of blue cloth in the shape of a heart sewn into the inside of the dress.