We report solvent effects on the piezochromic behaviour of wavelengths of maximum absorption for metal-to-ligand charge-transfer (m.l.c.t.) bands of several molybdenum–diimine–carbonyl and titanium or vanadium–cyclopentadienyl or ethylmaltolate–thiocyanate complexes. These and previously published data are collated in an attempt to establish a pattern for solvent effects on piezochromism of m.l.c.t. bands. Strategies for the design of compounds and complexes for use in establishing a clear pattern for such effects are outlined.