Dark is fine. In older cars it doesn't stay as clean. It should be a consistent color, no silver/grey, no metal shavings and shouldn't smell burnt. Some on the stick, where it passes the manifold (or block), will smell burnt. But the fresh stuff at the end shouldn't. It should just smell like hot oil. As long as you're changing regularly, you're good.
Remember when doctors used to rely on smell to help make diagnoses? Nah, me neither, but they did. :P