pixel_player378406685 These are the clues (notice the use of the words symbol or stone. symbol meaning the spot on the ground where the stone goes?)
The main bridge is opened with the green symbol.
The main bridge is opened with the beige stone.
The fisherman's bridge is opened with the green stone.
The fisherman's bridge is opened with the white symbol.
The southern bridge to the woods is opened with a red stone.
The northern bridge to the woods is opened with the blue symbol.