Tea powder gives red color in hot water,but some local tea powders gives red color in cool water why?

In mixes, the tea is routinely a minor component, with sugar the standard primary ingredient, plus flavorings, coloring agents, anti-caking agents, and so on. The consumer defines the product as tea.


http://www.teaandcoffee.net/0102/tea.htmTea powder gives red color in hot water,but some local tea powders gives red color in cool water why?
The dyes they use.Tea powder gives red color in hot water,but some local tea powders gives red color in cool water why?
The ones that give color in cool water have probably been brewed already, then dehydrated, so that any water will rehydrate it and it will become tea again.