Milk-lasters insist that one can measure the proper amount of milk to add only by watching the color of the tea change. Nonusers of milk, of course, regard the whole question as silly. Some authorities state that a small amount of sugar enhances the flavor of some black teas, with or without milk, and even some oolong teas. We have not found this to be the case, but that may be because we do not care for sweetened tea and find, as many people do, that it disguises the flavor of the brew. For that reason, we rarely add lemon, though the lemony nuance it adds does enhance thin teas.
Few people recommend adding anything but lemon to green teas.
In short, the addition of milk, sugar, and lemon is as much a matter of taste as custom. The question of what teas go best with certain times of the day is again a matter of custom and taste. Keemuns were the original English breakfast teas, but now that role is taken by hearty Indian and Ceylon blends as well. Oolongs go very well with pastries and other light desserts, and though most teas are drunk after meals, a cup of fine green tea makes an unusual and bracing aperitif. In most tea-drinking countries, the only meal with which tea is taken is breakfast, although tea is often accompanied by snacks.