The original stuff for your vintage is a yellowish colour.
You can top off with genuine Porsche coolant, which has been superseded by a pinkish coloured product, or risk the sky falling by using G12/G13 Volkswagen coolant (oh shock and horror) as I did when it was time to flush and replace my water pump.
I wouldn't risk generic auto parts store coolant for risk of gelling due to incompatible chemistry.
I couldn't tell the difference between the VW and Porsche stuff, they both tasted the same to me.
