Blue tint on window

My customer called and said that there is starting to be a buildup of a blue tint colour on there windows. I have never heard of this before. Just wondering if anyone knows what this is and how to get rid of it. I use dish soap and water to clean the windows. I went by today to take a look, but it was all cloudy out so I could not see what she was talking about.

Maybe they just never actually saw through the window before?


I was told once that that is from the manufacturing process. It’s really hard to get a pic of too btw.