I think a horizontal one would look cooler... wrapping from the outrigger posts around the port hole in the front.
sort of like --(--o--)--
where the -- and the 0 are blue. Sorry for the crude ascii art, my paint programs are on the HD raid that died.
Maybe 3 pixels wide would look good, with a 1-2 pixels wide as it goes around port hole
By making the line go around, rather then through, the port hole, it would serve to emphize it, and add a nice artistic touch.
But just some thoughts to play around with. I think the blue globe could stay all blue too... Alternately, make the globe a lighter shade of blue, as this would still leave the unit civ colored.
If you look at a CIV palette you will see there is a range of possible colors.
Using these different shades gives you parts of a unit with lighter and darker civ colors.