It certainly is feasible Chuck, but I believe the tops were made of soft wood, fir, and presumably they had the manpower to keep them tarred or blacked to offer some level of preservation.
A good question to ask the guides, which I will do on my next visit, trouble is they may invite me to go up and have look
As regards models of Victory, those that are painted that is, they are generally shown as having the upper sides of the tops also blackened. This accords with the colour scheme published by the Official Victory web site which does not note a variation between the various parts of the tops.
I have however seen a photo of the 'Constitution' from above which shows the planking of the tops a grey looking colour in contrast to the white rims and bottoms.