Advice please, henna?

Would a colour protect (Aussie) shampoo & conditioner actually help keep the colour in? or will it do the reverse and wash it out/change the colour because its meant (im guessing) for mainly chemical dyes? anyone know the real answer to this and can give me a reason why please i would be grateful. Ive tried google but didnt find much help. Thanks. Also its caca noir from lush. Love it :D