Mary-Kate and Ashley Olsen wanted to number their new fragrances.

The 31-year-old twins have launched their new perfumes named Nirvana French Grey and Nirvana Amethyst, and the stars have admitted they initially wanted to name their scents ''One, Two, Three'', before they decided on titles referring to colour.

Speaking to Allure Online, Mary-Kate said: ''We actually originally wanted One, Two, Three, Four.''

Ashley added: ''But decided to go with colour instead.''

And the 'New York Minute' actresses said the biggest ''struggle'' they faced was settling on a name for their products.

The fashion designers - who co-founded The Row as well as Elizabeth and James - explained: ''That was the struggle in the beginning, because we really thought we were just going to do Black and White. But then when we decided we wanted to do more fragrances. So then we had to ask ourselves, 'What does the bottle look like? What's the story we're telling?' If we continued to use solid colours, like Black and White, those would be quite shocking. So then it had to become a bit more transparent.''

Ashley added: ''We always wanted it to eventually become lighter...''

Mary-Kate continued: ''Become lighter and friendlier. It has evolved in that way. Even the packaging, the gifting, we've definitely evolved. And fragrance has such a long lead time as well. French Grey and Amethyst, I feel like we worked on them last year, so I'm happy everyone finally gets to explore and experience them.''

However the pair overcame the hurdles, and have admitted they enjoyed the ''whole experience'' of creating the cosmetic products.

Mary-Kate said: ''I knew that everyone took to fragrance differently, but I didn't realise how different a fragrance, like even a single note, sits on different skin. I could love it on myself and not like it on Ashley, or like something on someone else that I don't like on me. I found that so interesting. I love notes, I love scents, I like pretending I'm a nose.

''I like the whole experience. I like what it does to your memory and how you use all your senses, and the emotion that it strikes up, it's actually pretty amazing.''

''I think we like similar notes, like if you look at notes individually. Sometimes Ashley's more sensitive to things that are overly fragrant, so I like to break down every scent and know, what is the top note? The bottom note? I want to know how much water or alcohol is in each scent. If I don't like a scent, I take out a certain note to see if we like two scents together and then if not, we go back to square one. And then we smell every single musk note, every single sandalwood, every single peony, because there's so many different version of each note and they all react differently. Something that you like on its own, or that you don't like on its own, can be partnered with something else that makes it come to life.''

Mary-Kate and Ashley have hinted they are planning to expand their beauty range.

Ashley said: ''The fragrance is also in the dry shampoo as well, but yes, there are other things within of beauty that Mary-Kate and I are attracted to and have done a lot of research on.''