the other day when I was doing the compression test, I noticed the plugs are a little dirty, kind of brown, or was it black? I can't really tell.

Maybe it's normal or it's a little rich. well, how would one correct it if his car was running lean or rich?

how would I know for sure that my car is running rich or lean?

btw, will the car consume more gas when it's running rich? because I smell a lot of burn gas everytime when I start the car, much more than my 6gen accord

 

you cant tell lean or rich by reading the plugs unless you use a certain procedure.
but if they are brown rust color then your engine is running well.