The water used to brew the tea significantly affects the colour and the taste of a cup of tea. Tea brewed in soft water or permanently hard water (which contains CaSO4) appears brighter than if it is brewed in temporary hard water (that contains Calcium bicarbonate CaCO3).
High pH water that contains bicarbonate makes the infusion look darker brown due to the greater ionisation of the tea polyphenols. While lower pH as in lemon tea the infusion turns yellow. As for taste some teas are more suited to softer water such as the orthodox manufactured Assam leaf, while high grown Ceylon and CTC manufactured teas are better with temporary hard water.