One more way that I like to transition my pastel dresses into fall is to pair them with boots, especially brown ones (for some reason black and pastel isn't one of my favorite combinations.)
These particular boots are a dream come true for me. I originally purchased them in black from modcloth (here) and then found them in brown on amazon (here.) I have wide-ish calves and short legs so that combination usually makes boot shopping an absolute nightmare for me. There are some options with oversized shafts but they always end up making my ankles look huge. Since these lace-up (and the laces are adjustable, hallelujah! Whoever thought of decorative laced boots should get a knuckle-sandwich, geez!) I can widen them around my calves but tie them tight around my ankles so you can still tell that my ankles do in fact exist.
dress- asos (old) | boots - amazon | hat - forever 21