@Gork - There are no invisible part of the forum. That would sort of defeat the object of the whole thing. Interetsingly, the site went through an inspection process a few months ago, in order to comply with standards around accessibility, although I can't, for the life of me recall the catchy title of the Standard concerned. It is the standards the NHS and other very large organisations comply with.
I see others have suggested you adjust your forum settings, and on a previous post, I suggested if you were still having problems you could contact
[email protected] with example screen shots and someone there would try to help you on a 1:1 basis.
On Windows 10, there are various settings which can adjust how things appear on your screen. It could be useful to check those out, in case something got changes by mistake along the way.
Similarly on handheld devices, such as iPads or Android Tablets there are settings, usually designed for those with sight issues, which can make things appear on the screen - lighter/darker, brighter or even almost as a photographic negative.