This may not answer your query but, FWIW I have had exposed screws on two boats. On one, a Gulfstar 44 in which we installed teak battens to enclose the underside of the house, and we used black coated stainless screws; the effect was very nice. On the other, a Hinckley B-40 which came with mahogany battens lining the inner hull and fastened with exposed bronze screws; we also enclosed the overhead with teak battens but this time we used polished stainless screws. BTW, stainless screws can be polished to a mirror finish very easily using a power buffer and jewelers'' rouge.
If you care to see what the SS screws look like you can see them on www.picturetrail.com, enter member name jacobsladder, go, open album entitled Willow and scroll to picture of companionway or galley bulkhead. That will give you some idea of using exposed SS screw fastenings.
Hope this helps answer your question. I know there are screw coverings available but none seemed very "nautical" nor did they allow the ease of getting to what lay beneath. Please excuse me if I didn''t offer you help in "covering" your screws - it''s just that that may not be the best way to go.
One man''s humble opinion...