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