Sour Mix is a mixer, that should be light yellowy color and not green as you can see in the stores. It is used in many cocktails and in kitchen in general. It is made approximately equal parts lemon and/or lime juice and simple syrup (equal parts water and sugar).
I always make my own at home, because first it is actually cheaper, and why would you buy this shity green unhealthy product, when you cam make your own so easy and so fast. :)
Do you use sweet & sour mix at home? Maybe as a mixologist, or maybe as a cook?