My take on smoke color.
Just stright charcoal and you have white smoke - not fully lit.
Throw a peice of "smoking" wood on there and white smoke is good.
Throw a chunk of bad wood and you get yellow smoke. remove food, remove the bad chunk and wait for bad smoke to get out of system and try again. Yellow is resin burning out of wood (wood was not aged correctly.)
Gray/Black smoke - Grease fire.
Watch a video on the tube of how to home make charcoal and most will show the wood gas burning off and many show the yellow resin smoke too.
Current Smoker: Char-Griller Kamado