Abstract: A method including a collection expanding model for expanding a collection of items. The method can include upon receiving a user request from a user via a user device through a network, retrieving a target collection of one or more collections from a database. The target collection can comprise collection items, one or more collection styles, and one or more collection colors. The method also can include determining candidate items for the target collection based at least in part on the collection items of the target collection. The candidate items can comprise one or more complementary candidate items or one or more substitute candidate items. The method further can include removing a first candidate item of the candidate items from the candidate items when at least a dominant style of the first candidate item is not included in the one or more collection styles and/or when at least a dominant color of the first candidate item is not included in the one or more collection colors.