Anty--thanks for that.....just to clarify....Back2natural is fine to leave on for longer...it`s the proprietary coloring products that you have to `watch`..... they are strong and will really deepen the color quite fast , so no more than about 3 minutes for those, and they are not as `kind`to system hair as `Back2natural`..... coloring your system hair is not too tricky...just be careful to keep it off the lace to avoid permanently staining it, and `watch`the clock carefully if using proprietary products. Paul.