Green tea is originated in China.
Japanese priest who went to China to study buddhism introduced Japan green tea as well as Zen in 12th century.
In many Chinese tea the roasted leave are used and colour of tea gets light brown.
About 30 years ago Chinese Oolong tea became suddenly very popular in Japan supposedly for its healthy contents. Among the Chinese tea Oolong tea is more favoured in Japan than Jasmin tea or other Chinese green tea.
In Japanese restaurants or snacks in Japan water or green tea gets served always automatically, as much as we want, in free of charge.
There is a way to distinguish if it is a restaurant with good service or not.
I would say, if you get sencha it is good restaurant, if the bancha which has inferior quality and light brown colour is served, it is a normal restaurant.
If the hot water with slight tea like flavour and colour is served, you can already imagine before ordering how their meals taste.
Anyway, not like in Europe, we usually do not have to order drinks.
We have lots of green tea.
P.S. Some say that it is a key secret why Japanese live long.