i prefer to use a wire guage for plug gap, but it doesn't really matter. the color difference is because some plugs are (i believe) zinc plated and some aren't. not sure of the application reasons, but the plating resists corrosion.
It's not a bad idea to add a very small smear of antisieze any time you're screwing two different types of metals together. especially when one of those metals is aluminum. (head) very little is needed....
even though plugs come "pre-gapped", always check them. If someone dropped it, the gap can change, and the $1.25 a week, overseas child laborer may have had a bad day that day....
_____________________________________________
Oh.....It's on, Biotch.............