Provided are methods of applying a tissue marking to a tissue and rendering said tissue marking colorless when desired, comprising implanting into the tissue an amount of the tissue marking in sufficient quantity to form a detectable marking, said tissue marking comprising at least one colored compound comprising a thermally activatable fragmentation group and at least one infrared absorbing compound, wherein the at least one colored compound is capable of being rendered colorless by unimolecular fragmentation of the thermally activatable fragmentation group when the tissue marking is non-imagewise exposed by a source of infrared radiation and applying sufficient infrared radiation to a sufficient amount of the tissue marking to render the tissue marking colorless when desired.