The color formers and color developers combine upon exposure to {HEAD ~ an imaging force}, such as heat or {TAIL ~ pressure}, to form different colored visible areas on the sheet 
The color formers and color developers combine upon exposure to { HEAD ~ an imaging force } , such as heat or { TAIL ~ pressure } , to form different colored visible areas on the sheet
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH