Hiya John,
Unfortunately, right now there is no way for the SCC Pro program to calculate inventory based on any of the Optional Fields. In order for you to do inventory accurately, you would need to set those products up as separate entities rather than choices in one product.
Although that might seem daunting, you are able to very easily copy and paste an entire product box to create another product and just change the text that makes it different. This definitely saves a lot of typing. Also another thing to do is include links within each of them to each of the different weight/color variations (I would suggest putting the links into 1 first, get that particular product fully setup and then copy and paste that one for the rest so you don't have to retype or recopy/paste the links and any description code).
Although that's not the optimal way to handle it, it does do the trick nicely until CC decides to add this feature to their inventory setup for us (we're hoping to get this). The links to the different variations will definitely be just as helpful as being able to choose it in a drop down since the customer doesn't have to look for it, it's there at their fingertips.
Just be sure to label the links clearly so they realize it such as:
Get this item weight in Blue (this would be a link), Green (this would be a link), etc.
Get this item in 165g Blue (this would be a link, and so on.
Keep it simple and clear and it will work fine. Hope that helps.