Navigate to the Library via the Page Navigation Menus on the left, and select Products.
Search the Brand and then select the Product you want to edit. Once selected a popup window will appear. To view Inactive Products, select the SHOW INACTIVE button on the right hand side of the screen.
Here you will see all the details relating to this Product. If you look in the bottom left hand corner of the popup window you will see the Active/Inactive slider. Click on it and set it to the option you want to set the current Colour to.