Originally Posted by Trippy
and the only hidden button I've found so far is the one by the spa (that changes the colours)...

That button behind the spa floods the room with black light. Now you can see the 3 hidden buttons that were not visible before.

I'd like to close by quoting Bellegar's famous last rhyme:

"Cursed be the mother that bred thee!
The wench must have been a hell-spawned banshee!"