Green tea is unlike black tea in that it is meant to be consumed straight. These additives will only add unwanted calories or, with artificial sweeteners, disrupt the delicate taste.
There are also negative effects on health benefits. If you add milk or cream a protein, casein, binds to catechins and lessens their efficacy.
Green tea with milk is not a desirable method of preparation. Clear green tea is best.
This is particularly true with matcha. Recently "matcha lattes" and matcha mixed with juices and other beverages have become trendy. It is not good for health benefits and, with high quality matcha, it is not good for taste!
The main reason why Green stea is preferred over other teas is the high amount of antioxidants. When (dairy) milk is added, the proteins in it bind the polyphenols of the tea. Thus, the antioxidant power is reduced considerably.
Green tea is rich in many nutrients. EGCC, 1-Theanine, Amino Acids, Vitamin K, Vitamin C etc., Milk is rich in calcium and protein. When both the ingredients are combined, many of these nutrients will be lost or reduced in efficacy.
If you do want to prepare green tea with milk it is best to choose a non-dairy, plant-based option. Soy or almond milk.
High quality gyokuro, sencha, and matcha are delicious when consumed straight. Healthy and delicious. A win-win!