I am building nine 11" Dahlgrens at the moment for various projects. Four are Verlinden: 2x 1/32 and 2x 1/16 and five are completely scratchbuilt functional black powder: 2x 1/32 and 3x 1/16.
First off, the Verlinden Dahlgren kits are probably the best they have ever done. The barrel shape is a little severe at the edges and flares, but a little sanding will fix them. the slide carriages in both scales are near perfect. The "string and yarn" they include is useless and the instructions suck like usual, so check carefully before gluing anything, especially on the rear cross member. The best reference for these guns is the 1866 Navy Ordnance Instruction Manual, which is downloadable at:
http://www.gutenberg.org/etext/19058
Now as to colors: all the gun barrels I have found were semi-gloss black. Most of the photo references I have show the wood to be unpainted - appears to be varnished, possibly stained, assuming they are white oak. Bronze fittings are polished (wheel brackets) as are the nuts and trunnion caps. Iron straps appear to be flat black. Best I can figure out, the trucks are solid iron, not iron strapped wood.
Remember that these guns were pampered by their crews - they had lots of time to clean them and their lives depended on them. Plus I'm sure there was stiff competition between the crews on ships with multiple slide carriage Dahlgrens as to which one looked and operated the best.
Good luck
