You do understand that charcoal briquettes burn from the outside in, right? The ash on the outside just signifies it's ready, there is still unburned fuel in the middle of that briq which is being lit and burned as it progresses. Kind of a micro-minion. As the O2 and heat hit deeper and deeper into the briquettes the fuel lights. If you want proof of that just knock the ash off of any lit briq or look at what's left in your grill after the cook. Ashed over does not necessarily mean that all of the fuel in a particular chunk is lit. If it did, they wouldn't last very long, they'd be gone in...if you'll excuse the term...a puff of smoke.
The key is to keep the fire properly ventilated for nice thin smoke. Heavy dark smoke is unburned fuel, basically soot. Light smoke is a more efficient burn with little or no unburned fuel. This is the same with wood. If you get a lot of dark heavy smoke for some reason, please stop, rinse off the food, and start over.