

The green layer is a solder-mask, and is used to make a finished board
look neat, and to avoid solder bridges, especially when using wave
soldering (or any other mechanized approach). I've seen red mask,
but most that I've seen are green.

A bakelite board will look brown in colour, and, if the solder mask
is put on, looks like a brown board with green 'paint' on either side
(or just one side) of the board.
A fibreglass board will look green from the side, because the green
solder-mask makes the board appear that colour. If you got a fibreglass
board with no mask, it would be a whitish-grey colour.
Teflon boards do exist, as well... but I'm not sure about that one.