My old Airbus is prone to ice on the exterior of the Outer fuel tanks.This happens on even quite temperate days and we don't fly very high so are not exposed to very low temperatures or for 10 hours!The only way to stop it forming is to create an air gap in the tank by feeding fuel from that tank,so that some warming can take place in the descent.Many times I have sat on a very warm ramp an hour after landing and still seen ice on the skin in the tank area.There is no indication of fuel temperature in the cockpit.Cold soaked fuel takes a long time to warm-certainly more than the 30 minutes a 777 would take to get from top of descent to the ground.