Anthocyanins, and the colour change
The pigments in butterfly pea, blue mallow and hibiscus respond to acidity, shifting through blue, violet and pink as pH falls. Adding lemon to butterfly pea turns it pink instantly. This is a reversible chemical response rather than a trick or a sign of spoilage, and the same pigment class colours red cabbage and blackcurrant.
Betalains, and why beetroot browns
Beetroot’s red comes from a different pigment class that breaks down with heat and time. A beetroot blend is dramatic in the first minutes and brown-pink twenty minutes later. Nothing has gone wrong; the pigment is simply less stable than hibiscus’s.
Where colour is added deliberately
Calendula and cornflower are in a great many blends for appearance and contribute essentially no flavour. Safflower has been used to make things look like saffron for a thousand years. Dried beet in a modern tisane blend is a colour ingredient with no drinking tradition behind it, and TeaHQ’s record says so.
What colour genuinely tells you
In roasted grains and roots, colour reads roast depth directly, and roast depth is most of the flavour. In flowers, colour reads drying care: a brown chamomile disc or a grey-green leaf was dried too hot or stored too long. Those are useful signals. The colour of a finished cup, by contrast, tells you very little about quality.
One thing colour does not tell you
Strength. A snow chrysanthemum brews a deep red-brown from three flowers and is a light drink; a pale mugicha can be substantial. Judging dose by the colour of the liquor is the commonest reason people under-dose roasted grains.