Smokeless or black powder produce volumes of white smoke when they're ignited in quantity - true HE when detonated produces black smoke.
I am not so sure about that - I have a vague recollection about reading a Biggles story as a kid which mentioned in passing that they could tell the difference between the German and British AA artillery explosions from the colour of the smoke, and presumably both would have been using High Explosive.
e.g. here:
https://books.google.co.uk/books?id...GjAC#v=onepage&q=biggles archie smoke&f=false
A cloud of white archie smoke had appeared just in front of him. White archie! Only British archie was white! Why were they shooting at him? The answer struck
The author had been a WWI pilot so presumably he'd based that on his own knowledge