Opaque green tea, what is that?
If it's &quot;green tea powder&quot; it's probably matcha.

Matcha is finely ground powder of specially grown and processed green tea. It's special in two aspects of farming and processing: The green tea plants for matcha are shade-grown for about three weeks before harvest, and the stems and veins are removed in processing.
The traditional Japanese tea ceremony centers on the preparation, serving, and drinking of matcha. In modern times, matcha has also come to be used to flavour and dye foods such as mochi and soba noodles, green tea ice cream and a variety of wagashi (Japanese confectionery).


The drink you had in Thailand is probably an iced matcha shake of some sort, made with condensed milk.  In Japan, the drink is served by itself as part of tea ceremonies and is opaque even without milk added to it.
There's a guide to how tea ceremonies work and the process of making tea here, if you're interested.