An improved color EP (laser) printer is provided for use in high humidity conditions. A humidity sensing circuit determines if the print quality might be degraded due to environmental conditions, using a resistivity sensing circuit, or a humidity sensor. If the print quality would likely be degraded, the invention is able to enhance toner transfer by printing supplemental process black toner dots underlaying standard black toner dots at predetermined pixel locations in the bitmap of a print job. This assumes that the black printing station is the "last" station along the travel of the intermediate transfer member. Other colors could be used for the supplemental toner dots.