I have heard that in ww 2?

i have heard that in ww 2 that american pow's taken by the japanese that the ones with red hair were treated much more harshly than the other pow's. i have heard this personally from veterans and have read and seen tv shows saying the same thing. i was wondering if anyone knows the reasons for this. i don't like to ask too many questions of war veterans as i don't know what will upset them.