In my experience the SCOBY both filters the tea (you'll find flecks of tea like pepper appear in it) and is ultimately stained by tea. Older SCOBYs will darken all over while younger ones appear to have spots and dark areas.
Tap: DIPA, oaked Baltic porter, XXX pale ale, dark IPA
Bottle: vanilla kombucha, oaked puh-er kombucha, blueberry kombucha,
Primary: rose hip kombucha, oaked honey and oolong kombucha, hopped kombucha brewed with green tea infused with cab. grapes