there's a reason professionals have to pass both practical and theory exams when learning about colour. Hazardous chemicals are used and they need to be fully understood before using on anyone.
It's when non-professionasl start meddling and guessing what chemicals are used for that hair disasters happen and the poor professional has
to sort out their mess, if you're not a hair pro and don't understand the
health and safety and science behind changing hair colour, please just
don't have a go yourself and leave well alone.