The signals you describe (I think) are ground position lights (or 'dods' as we call them).
The top colour is white, and when in the off position, the red aspect in the bottom left goes out and is replaced by the white light in the top position.
Giving a white: \ \
Just because they are triangular, doesn't necessarily indicate a turnout, they usually are placed either on a turnout, or where you proceed over a trailing junction (where a route indication isn't necessary). They are basically used in place of a full signal because they are a lot cheaper and easier to use.
The can also be used as position lights on main signals indicating permissive working, and can have different colours (two red aspects on the bottom row = limit of shunt) to show different things.
Hope this helps