It's clear that you're wanting to add some interest to your engine compartment vs using OEM color choices, which is one of those " It's your car, it's your choice" things. For me, I wouldn't paint a Ford engine "Chevrolet Red-Orange", regardless what the complementary color wheel shows, and Firebird's story of painting bolt heads, valve covers, and belts(???) different colors just wouldn't work for me. I know it wasn't for you, but Tech's selection of the early Cobra engine would look great, to me. If you're wanting pop, how about a nice, bright yellow?

You might go to your local paint store and pull a card that matches your "medium dark blue", and compare to other colors to find what pleases your eye. Your auto paint store can mix up a good auto paint to match, and then you can either have them put it in a few rattle cans, or use one of the PreVal type sprayers.

Google "Complementary Colors" and read up on how to pick colors that complement, contrast, or harmonize. Or just let your wife pick the color..... but tell her no pink, no purple