WHEN word spread of the sensational discovery of the well-preserved Roman towns of Pompeii and Herculaneum in the 18th century, ''Pompeiian red'' became the favoured colour for smart dining rooms - as it remains today.

But, it seems, it may be time to get out the paint chart.

An ancient Roman fresco depicting the cult of Dionysus in the Villa of the Mysteries in Pompeii. Credit:The Art Archive / Gianni Dagli Ort

Research presented to Sapienza University in Rome concludes that large swathes of the vivid Pompeiian red frescoes in the town actually began life yellow - and were turned red by the gases emitted from Vesuvius as it erupted in AD79.

Experts have long realised that some of the characteristic vivid reds of the frescoes in Pompeii and Herculaneum were originally yellow. But a new study, conducted by Italy's National Institute of Optics, suggests the sheer extent of the colour change.