I am looking to the windowed roof of my building, and I notice that the sky, which has few white clouds, sometimes looks completely gray, as if there was a huge cover of gray clouds, but there are not.

By observing it and waiting for the change to happen, I notice it takes a matter of seconds : when the sun shines directly on the building (but not directly on me), the blue sky turns gray. I wonder if this is just an optical illusion because my vision of colour could be relative to its environment, or if there is serious glass/sun/refraction effect or something. I haven't found anything on that matter on the internet or on Stack Exchange, so I'm asking you what you think about it.

Additionnal information : The top window is a very peculiar glass, it's basically a strong glass window (because it's almost horizontal, it has to resist hits) and looks like it is covered by a layer of opaque black, with big holes (surface of holes is greater than surface of black, from a distance you don't see the holes). Also, I'm taking the pictures from a windowed office, you see the sky through two glass windows, but the one closest to me looks basic and I didn't notice a difference when looking through one layer. You will also notice there is a blue light, some neon-like directed at the roof, but during the day its effect is negligible.

Here are the pictures, first the sky through top window without sun hitting the window, then with the sun (The colours/ exposition differences don't seem to make a great difference compared to my naked eye observation. The pictures were taken only a few seconds apart, you can see the same cloud in both pictures. The gray sky isn't the most grayish I've observed, it gets even farther away from blue sometimes) :

I am looking to the windowed roof of my building, and I notice that the sky, which has few white clouds, sometimes looks completely gray, as if there was a huge cover of gray clouds, but there are not.

By observing it and waiting for the change to happen, I notice it takes a matter of seconds : when the sun shines directly on the building (but not directly on me), the blue sky turns gray. I wonder if this is just an optical illusion because my vision of colour could be relative to its environment, or if there is serious glass/sun/refraction effect or something. I haven't found anything on that matter on the internet or on Stack Exchange, so I'm asking you what you think about it.

Additional information : The top window is a very peculiar glass, it's basically a strong glass window (because it's almost horizontal, it has to resist hits) and looks like it is covered by a layer of opaque black, with big holes (surface of holes is greater than surface of black, from a distance you don't see the holes). Also, I'm taking the pictures from a windowed office, you see the sky through two glass windows, but the one closest to me looks basic and I didn't notice a difference when looking through one layer. You will also notice there is a blue light, some neon-like directed at the roof, but during the day its effect is negligible.

Here are the pictures, first the sky through top window without sun hitting the window, then with the sun (The colours/ exposition differences don't seem to make a great difference compared to my naked eye observation. The pictures were taken only a few seconds apart, you can see the same cloud in both pictures. The gray sky isn't the most grayish I've observed, it gets even farther away from blue sometimes) :