Please educate me

I work at a store which (Australia wide) is a big supplier of engine coolants.
Thus I regularly have the questioned asked "Which is the right coolant for my car"

Now I understand that there are 3 main/retail coolants, Type A, Type B and the Pink/Red stuff (not so sure on the name there).
Type A is for Alloy blocks/heads (modern) and Type B is for old Cast Iron blocks/heads???

Could anyone please educate me on these Types?
Thankyou