Herbal infusions can be genuinely spectacular in a glass pot, and this collection gathers the plants that do it. Cornflower petals hold a real blue, calendula turns an infusion deep gold, and viola gives violet. The best of them is red shiso: its anthocyanins are pH-sensitive, so a shiso infusion is a deep purple that flips to bright pink the moment you squeeze in lemon. It is the same chemistry as butterfly pea flower, and it is a small piece of theatre you can do at a table.