Bruce Culver's Panzer Colours has a section on "method of application". It states that the engine-driven spray gun was the most common method of application and other methods were sponges, brooms, mops, rags, hands and throwing buckets of paint or whitewash. The photographs on that page of the book show a King Tiger receiving an immaculate spray job using the engine-driven spray gun, a Sd kfz 250 having thick paint daubed on with a relatively small paintbrush, a Horch(?) personnel car being whitewashed with yard and straw brooms, and a Sd kfz 232(?) having paint applied with a sponge and bare hands.
The book is full of photographs showing how variable the camouflage finishes are . . . and then there are the other two volumes in the series.