U.S. Pat. No. 4,756,758 to Lent et al., which describes thermochromic jet ink compositions which are formulated to contain two different dyes and having a resin such as a phenolic resin, a solvent liquid carrier system (e.g., based on a lower aliphatic alcohol and a lower aliphatic branched ketone) and, optionally, surfactants, plasticizers or the like, and wherein the compositions have a viscosit