What color's is hidden in forums can you please tell me HIDDEN FORUM COLORS?

Answer 1

Someone is perhaps playing a trick on you? Normally, all forums can use all colors. None of them are hidden.

There are page builders where you can choose to MAKE a color be hidden to allow for transparency (perhaps to show a picture behind a forum display element). But it is arbitrary as to which color you choose as your hidden color. That is, it can be a specific shade of gray on this page, black on that page, and yellow on another page. No one color is always hidden.