You may notice some new buttons in 3-Up and 1-Up views in the View Catalog Page. 

These buttons will allow you to add a colorway to an existing shipment in your order. Simply click on the shipment and the product will be added to it.  If you don't see these buttons, don't worry! This means your order currently only has one shipment. You can add multiple shipments to your order on in the 'Build Order' or 'Enter Quantities' pages.