colouring over henna?

[StepAwayFromTheEcclesCakes]

has anyone done this? I used Lush Brun henna but my roots are still noticable can I use my usual home colour on them or will my head explode

just in case anyone is remotely interested I found out that Lush henna is safe to colour over because it does not contain any metallic salts heres hoping my hair stays on my head and does not go green!