Are we talking space marines or imperial navy?
If space marines:
The larger space marine ships have round spaces where you can actually put the GW transfers and painting ships in recognizable chapter colours looks nice.
If you want to go fast and easy, with a colour that is normally impossible to paint, Imperial Fists have a yellow colour scheme. I use army painter yellow undercoat and medium dip, which works extremely well. (I could make some pictures if your interested) the dip medium would bring out all the fine details of the ships very nicely and safe you a lot of work.
If, on the other hand, you are talking about imperial navy, I find the standard green with white and gold bow very good looking. For this I used a black undercoat base layer of dark angels green and drybrushes with snot green and goblin green.
the bows take a layer or two of foundation paint to get white but it looks quite striking.