Is it just me, or does this version of the Enterprise have a metallic bronze hull color? Very Flash Gordon.
(Or, depending on your SF tastes, very Forbidden Planet.)
So much for "this we will not do", eh?

The same "proto-Enterprise" design shows up in several similar Matt Jefferies drawings, all viewable at Forgotten Trek. Interestingly, one of these is in color, and shows off the shiny bronze-hued hull.
Evidence suggests this was more or less the design that Jefferies turned into a small model, to show Roddenberry and the studio executives what their starship would look like.
David Shaw has pointed out that the early plans Jefferies made for the Enterprise filming model (then assumed to be about 540' in "real world" length) had no windows--the view ports were added only later, after the fact, onto a subsequent set of plans for a much larger ship. I wonder if, when Jefferies' early 540' windowless plans were made, the "shiny metallic hull" idea was still in place?