The stuff you are refering to is yogurt mint sauce. I make my own yoghurt as its sweeter than the bought stuff and it thins out when its blended.
for the yogurt:
i pint of milk
heap tbs live yogurt
boil milk
cover pan and cool till luke warm (40 degrees c if u got a thermomiter)
now stir in yoghurt and stir in along with skin that has formed.
pour into a warm non metalic container/bowl, wrap in towels to insulate and leave in warm place for 4 hours, If using for marinade leave for 6.
for yoghurt mint sauce
2 cups of home made yog
2tbs colemans mint sauce
half tbs amchoor powder
tbs or 2 chopped corriander
garlic puree (optional, to taste)
half tsp kashmiri masala
pinch salt
small amount of food couloring(yellow or green if you want)
sugar to taste
check the taste,
chuck above in blender and give a few short blasts.