A solution of α-crustacyanin subjected to three cycles of heating to 70 °C and followed by immediate cooling at ambient temperature showed that the colour shift ability was not compromised by this treatment. Fig. 4 shows the natural spectrum, the shift from 525 to 490 nm on a third heat cycle to 70 °C, and the shift after a final heating to 90 °C where the maximum is at 480 nm and irreversible.