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