Thanks for your reply. Seems like I solved the issue lol. It was so simple.
I was trying out different monitor settings and there was an option called "black level". It was set to low as default.
That was it. I tried changing this option to high, problem solved, I can see the light grey on the site's background again, as I normally did before. Can you or someone please explain what black level does and if it should be set as high? I don't know why it was set to low as default, I never changed it.
Not only that but now I see so many colors differently. For example, the facebook poll I mentioned, that had light blue bars, I was seeing that light blue color so wrong, it was almost like white. Now, what a difference, the bars are light grey but the difference to the white background is huge. Night and day. So better now and easier to distinguish.