Jada Joyce, after Tibi, NYC, September 2015.
A simple, beautiful way to dress up a simple slip dress — add a print neck scarf. A rich jewel-coloured slip dress (or even a lovely print — Topshop have a gorgeous palm print slip here) would work beautifully with a scarf for the middle of summer. 
Recreate Jada's look (kind of):
Topshop Tall Cross Back Slip dress, Equipment Prue washed-silk mini dress, Sincerely Jules Capri slip dress, ASOS Mini Slip dress with eyelash detail, Alice + Olivia Fierra stretch silk slipdress, Vetements Structured slipdress, Pieces Patrizia Slip dress, Helmut Lang sleeveless voile slip dress, or The Row Aneme silk-satin mini dress
Skinny scarf — Valentino Printed scarf, Topshop Star skinny scarf, Gucci Fringed printed scarf, Rockins Super Skinny scarf, Topshop College Stripe scarf, or ASOS Skinny scarf