Gwen Stefani working on lipstick collection

Pop star Gwen Stefani is developing her own line of lipsticks.

The Hollaback Girl hitmaker, who was appointed a L'Oreal cosmetics spokesmodel in 2011, reveals she has been testing a range of different brands to help her come up with the perfect product.

Showing off a test formula during a MasterCard event in Los Angeles on Tuesday (20Jan15), she told People.com, "I am working on some lipsticks. This red that I'm wearing right now is a prototype."

Stefani, who is known for sporting a bright red lip, has yet to reveal further details about her make-up plans, but she is no stranger to the fashion industry after previously launching her L.A.M.B. clothing and shoe line and her Harajuku Lovers perfume collection.