I recently moved to a new house which has 2 speakers installed in the roof of the patio. Inside there is a wall plate which has the satellite connections; phone and a grey cable with four coloured wires black, red, green and white and this (I am told) is the means of connecting the speakers to the internal amplifier or whatever. I have no idea how this would work?

Macplac

Four-color wires SOUNDS like speaker wires. Are you saying there's a pair (left and right) of these 4-wire wires? My surrounds are bi-wired with this type of wire. Yup, those would connect to your power amp or receiver depending on your set up.

Thanks. It's a question of deciding which are the pairs?

This is a very common color code for 4-wire speaker cable:
red: R+
black: R-
white: L+
green: L-

Been common, a de-facto standard, for decades. I am wiring using 4c speaker wire right now, the cable follows that color scheme, and that's how I'm connecting it up too. You'll notice on most gear with colored RCA jacks that red is R+ and white is L+. When you only have two wires, like for DC or speakers, black is usually the - when paired with red. Thus that leaves green left over, so we make it L- to make everything "common" fit together.

Edit: what I meant ^ is if you have to "guess", this is most likely as it's commonly used in the pro (stereo) audio world.

Thanks..I'll have a go..