It may be hot and humid outside, but stores are beginning to fill with fall merchandise. The emerging shoe trend: colorful, comfortable oxfords, a welcome evolution from the ubiquitous ballet flat. Pictured, left to right, are four stellar lace-up examples from Opening Ceremony ($322; 212-219-2688; available in August), 3.1 Phillip Lim ($410; 212-334-1160), Topshop ($125; 212-966-9555), and Kaight ($99; 212-680-5630).