Advertising was printed on a fair number but not all New Zealand stamps of that period. This started in 1893, done on values up to the 1 shilling. Stamps in a sheet would have different ads in different quantities.
Specialist listings exist. There are at least a couple of colors. Some designs are common (Sunlight Soap) and some are scarce.
EDIT: This shows the layout of one setting of one pane, image from a Campbell Paterson New Zealand catalogue. Windows Update killed the scan setting on my printer, so I coudn't do this earlier. Note several styles of the Beecham ads.