Why might a person not be able to see coloured ink on a whiteboard?

25 October 2010
Presented by Diana O'Carroll.

Why might a person, who apparently isn't colour-blind, not be able to see red or green on a whiteboard? What is colour-blindness anyway? We try to find the answer in this Question of the Week. Plus, we ask which is worse for the environment - a few weeks of volcanic eruption or a few weeks of aviation.

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