Gas detector paint

[alan.moore]

If you look at the top of the headlamp and the front of the mudguard you will see lighter areas of paint. I have read that this is 'Gas detector paint'
(Vesicant detector paint) which was applied to motorcycles and other vehicles so that it was visible to the driver/rider. It apparently changed from a greenery/ yellow colour to red if exposed to a chemical warfare gas such as mustard gas and Phosgene gas.

I have read that it was also painted on the top of Post Office pillar post boxes in some areas of the UK during WW2