It's related to some armour sets after Darklight went dyeable getting the metallic shine when you dye them. DRG AF is one of them, hence why pure white turns into light silver as you say it. It's basically the actual pure white + metallic shine = light silver.
Until they put in some sorta option to allow us to say "Okay, I see you get dyed with a metallic shine by default but I'd rather you don't" that's sadly how it'll have to be :(
