The 30-year-old actress recounted of her disastrous experience when she applied a heena based colour to her hair which gave a green tinge to it, reported Femalefirst online.
"I once used henna to dye my hair brown for an audition. Little did I know it was the worst thing I could've done as it coats the follicles so nothing else can penetrate and I ended up having to put ketchup on it for about a year to get rid of the green tinge," said Miller.
Due to the constant experimenting with her hair, Miller said it needs a careful regimen to look after it.
"Because I have to mess with my hair so much for work it gets pretty dry and I'm constantly looking for products to put back the moisture," she added.
Miller is expecting her first child soon with fiance Tom Sturridge.