The results of a systematic study of the influence of the color developer and the solvent on thermochromic properties of a reversible thermochromic system-crystal violet lactone as dye; propyl gallate, octyl gallate or lauryl gallate as developer; 1-tetradecanol, 1-hexadecanol or 1-octadecanol as solvent-are presented. Thermodynamic analysis of the developer-solvent phase diagrams is used to determine and compare the developer-solvent interactions in the systems, and observed variations in thermochromic properties are correlated with these interactions. The relationship between thermochromic behavior and competing dye-developer and developer-solvent interactions leads us to the first design rules for reversible thermochromic mixtures based on intermolecular interactions. (C) 2005 Springer Science + Business Media, Inc.