Not sure about P-40s but there is a definite provenance to desert theatre machinery being pink. For example the British Long Range Desert Group (later to become the SAS) had sand finished long wheelbase Land Rovers that had the nickname "Pink Panther". In addition, the sand colour that British Jaguars and Tornadoes were painted in for the Gulf War in '91 has a definite pinky hue - to the extent that the specialist model paint manufacturers actually refer to Gulf Pink in their product descriptions.
example:
I believe the pink hue in sand is a result of the silicates in the sand picking up and reflecting light.
cheers
Rick