When you hold a certain piece of glass up to the light

[bukie33613]

When you hold a certain piece of glass up to the light...

Hi,
My question is thus:
When you hold a certain piece of glass up to the light, the light coming through it appears blue. But when you shine light on it, it has a yellow color. What's going on?

 

[brum]

But when you shine light on it, it has a yellow color.

what's the "it" referring to? the piece of glass? the particles in the air reflecting the light?

 

[mouseman]

I am guessing he means the glass, and by that I would say he is speaking of reflection and refraction. As bukie never mentions the original color of the glass as seen by "white" light, I am also assuming that the color of it is one other than "clear." Now correct me if I'm wrong but the shape of the glass would have to be something other than "flat" in order to cause it to appear "yellow" when the light is reflected off it, and "blue" when light passes through it.
I'm afraid you're going to have to be alittle more specific in your description, bukie.