This is Not a feature of ALS as far I know.
How mobile is he?
Is this a recent change?
What is the temperature of the hands and feet like?
Is there swelling?
My dad too was diagnosed with ALS in November of 2016, and before this I had noticed that his right leg, which was the drop foot side, had a really white color to it as well...and obviously was small in size.
He is still active. Still working. ( General Manager of a company). No swelling of sometimes cold sometimes not. It started with the hand most affected then to the other and now the toes back to the arch. Thank You For Responding