Hi JWS,
I have figured out the easiest way for you to carry over the newly created value from your Estimate screen, over to the Sales Order Screen.
Keeping what I have already mentioned from above, we have created a new dropdown field, "SidingColours" from the Estimate Table. Then I would suggest creating a drop-down field in the SalesOrder Table with the same name, and make sure this one is based of the existing table created when you made the original "SidingColour" drop-down (refer to screenshot below):
Now go to Customize the Estimate Screen, you will need to edit the actions I mentioned in the above post as a hint, so go to the More Actions->CreateSalesOrder Button, and look through the actions until you find one labelled "Insert Records Into Table" with the note "Insert the SalesOrder record from the Estimate, getting back resultRecordID", edit it, and add your new "SlidingColours" field…refer to screenshot below, but follow how the others were done here:
Once you have filled it out similar to my screenshot, click "add" and make sure it is now on the list below. That should be it, provided you have already added the "SlidingColour" dropdown fields themselves to both screens, when you select the "CreateSalesOrder" button from the Esimate Screen, the Siding Colour chosen here will be carried over to the Sales Order Screen, along with all the other information. Please let me know if this helped, and feel free to ask more questions if get stuck along the way.
-Ben