Silver doors are locked doors that contain a special loot chest.
Poelab locked door.
They are indicated with a grey door symbol on the labyrinth map.
These are not required to progress through labyrinth and are only optional.
You must follow the pattern located on the floor outside the puzzle room.
Be sure that the pressure switches are being triggered and remember you cannot trigger switches diagonally only the adjacent ones.
A silver key is required to open this door.
I just look for the intersection of these 2 side by side doors.
This will open the door and is the combination for this puzzle.
This is one way to find 1 variation of hidden switches in the labyrinth.