You'll find that with most of today's gas, that plugs don't "color like they used too". It is difficult to achieve a nice chocolate brown color . . . just never seems to happen for me. I tend to see colors that are a much lighter brownish/grey when the mixture is right.
As RoTo mentioned, you should do a test on the highway . . . is the only real way to do it. If you drive around, then come to stops and idle the engine . . . you'll find they almost always look too rich. So, you can't check the plugs after you go home - you'll not have accurate coloring . . .
Or, put some O2 sensor bungs in your exhaust and use a meter to tell you what is really happening.
