You could probably have each size, color, and product combination as a separate product so that you wouldn't need to update the current inventory control system.
Trying to do inventory control for multiple options will get very hairy very fast if you don't insert them as separate items.
OK I can see how that might be the better solution for us mere mortals but when the customer comes to the item in question – a shirt let's say – in one particular style and design that is available in 6 sizes and 4 colors each size thus necessitating 24 separate entries into the db how do we logically represent that to him or her as a single item available in a myriad of sizes and colors?
I know I'm not the only one confused by this.
Wouldn't it be easier to have a color and a size table and incorporate them as foreign keys.
I've mimicked your "productcategories" table in PowerStore to create a productsizes and productcolors table and have attempted to emulate what you did but so far, no luck.
Either method of getting the job done would be OK with me but am I wrong to assume the latter method to be the preferred one?