If you run out of an item, you should celebrate! As far as your Item Listing is concerned, you have nothing to worry about (as long as you had your Inventory Tracking turned on). If your Inventory Tracking is on then the system will know that your inventory has been depleted and will no longer display the item in the size and/or color that is sold out. If all your inventory is gone, then the listing will no longer accept payments and will display a ‘Sold Out’ sign where the Purchase button was originally displayed. This will give you plenty of time to either go into the system and unpublish the item (and possibly restock) or let it stay visible so you can beam at your accomplishments.