That's weird looking. What's the inside of the boot and spring look like? Same thing?

 

I just changed my 4.6 spark plugs for the first time @160,000 miles. All the plugs had an orange tint on the tip like the one in the photo you posted. I scraped the tip of the plug with a pocket knife to see if it was rust and it was not. I would say it's normal. Probably caused by the voltage being passed from the spring to the spark plug causing discoloration. That's my guess but could be wrong.

 

All the coil packs had a yellow paint mark on the top of it