Fugitive pigment is a phrase used to describe a pigment's impermanence and tendency to fade or change colour under the influence of natural effects such as sunlight, heat, water, etc.

Reynolds famously has many portraits that have lost the skin tones because he used Alizarin crimson which was a fugitive pigment, however, modern Permanent Alizarin crimson has a permanence A.

AA – Extremely Permanent

A – Permanent

B – Moderately Durable

C – Fugitive.