All three core SWA will use the harmonised colours as per the photo. You wont see any with brown, blue and green&yellow cores like you see in normal flex. Before the harmonised colours change it was Red, Yellow and Blue.
You can buy two core but far better to use three core and use one as live, one as neutral and one as earth. You can leave the brown as brown for the live but the other two should be sleeved with the correct colour sleeving as soon as they leave the cable, blue for neutral and green&yellow for the earth. It is not really good practice to use the armour as earth since it is steel, not copper, so has far different electrical characteristics and also the integrity of the earth path then relies upon the mechanical contact between the glads at each end of the cable and the armouring wires.
This is why it is quite common to see a spearate insulated copper earth conductor running alongside three phase SWA cables (where all the cores are in use).
For single phase it is far better to use the third core as earth
Make sure you earth the armour as well though since, as well as providing mechanical protection, it also provides electrical protection if something conductive penetrates the cable and hits the live conductor (like a spade with you holding on to the other end) as that conductive object will also be in contact with the earthed armour and will therefore provide a nice low resistance earth path and trip the protective devices before you get a nasty shock.
