The new site features that enable sellers to list multiple sizes and colors--variations--of the same product in a single item are now active in Mens and Womens Shoes. In July, multi-variation listings be available in the rest of CSA and most Home & Garden sub-categories.
When shopping, look for the "More Options" link below the title in search results to identify multiple variation items. Mouseover that link to popop a summary of the variations included in the item. On the item page, use the new drop down boxes to select the variation you are interested in purchasing before you click the Buy button. There is no need to message the seller to specify the variation you want; they see that information automatically when looking at their sold items.
For those who missed the April announcement, here's a link to all the details:
Multi-variation fixed-price listings FAQ Augy
eBay