Keeping chain clean

I have been wiping my chain, rear gears and front rings down after every ride.  I want to be sure they are nice and clean.  The chain is "silver" and the gears are all "silver".  When they are really clean, they look great.  When they are dirty , not so much.  I learned here that  a clean drive train is a smooth drive train.

I was out for a really dusty group ride the other night, and when I got home,  I saw I had the newbie  oil smear on my leg.  We had stopped to regroup a couple of times and I had laid my leg on the front gears while resting. It was a giant smear.  I was bummed.  I thought I was doing a good job of maintenance.

I was out in the garage ,just now, running the chain through a rag while cranking the pedals backwards.  There is no visible goo on the rear gears, or the tension wheels on the rear derailer.  However, If I keep runnning a rag over the chain, I still get black on the rag.  It diminishes the longer I do it. 

So the questions are, "How clean should the chain be?"  "What should the rag look like on a properly cleaned chain?"