Botanical colouring, natural colouring, or plant colouring are different names for dyeing with plants. All with the objective of having a toxic-free or almost toxic-free dyeing process.
When I was a ceramicist, I was very interested in the way colours are produced.
I made my own coloured slips for years and when I wrote my article about the different colours of clay my interest in natural colouring, in general, was aroused once again.