Hmmm. That's a good question. I'm thinking the bottom one is a little more accurate as far as the battle cruiser is concerned. The top color looks more appropriate for the attack "bug" ship. Then again, color, like scale, has never been Trek's strong suit. Everyone thinks the Romulan Warbird is green, but the filming model was really very gray, with just a hint of green. These ships were lit in such a way to give them different color temperatures. Federation ships often seemed to look blue, Klingon ships gray and green, etc. Of course, CG ships had a different set of coloration, so it's difficult to nail it down. When building models, people sometimes tend towards how they "appeared" on-screen, rather than real life, so maybe the top one is more accurate.