Hi
Sorry for late response, I just saw this post. Here is the answer.
What you have to do is to go to product attribute page. On the top left there is product option table. Ist colum is ID, 2nd is option name, like colour and size. the 3rd colum is for Track stock? Check this colum infront of product option you want to track. If it says 'No' then click the edit button and check the box to change this to yes. Go back to admin catalog menu. Click stock button infront of the product you wanted to amend, it will show you all attributes in the next page, select the attribute by drop down window enter the quantity and press add. Thats it! You can go to Admin Report menu where you can see the stock as per attributes. I hope you will find this useful.
Cheers!
Sohail