In one embodiment, {HEAD ~ coatings} of initially colorless color formers and {TAIL ~ color developers} are coated on selected areas of a substrate surface 
In one embodiment , { HEAD ~ coatings } of initially colorless color formers and { TAIL ~ color developers } are coated on selected areas of a substrate surface
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH