Greg: I'll take a stab at your question about black/white stack smoke.
I surmise the black smoke is produced as coal is being augered into the firebox to feed the fire under the boiler. As the fire "settles' itself after being churned by the coal feed, the fire starts burning cleaner as more oxygen helps the combustion process leading to more complete combustion and less un-burned coal. This leads to "less-black" stack gas, or what we perceive as "white' smoke ( or sometimes near-clear...).
"Sanding the flues" would also result in darker stack smoke as well.