I tan quite easily so I find myself mixing foundations to match my shade pretty often. It's impossible to live in Los Angeles and only have 1 foundation. When I've gotten a little sun, I can use my Bare Minerals Gel in 7 Tan on it's own. It's a great everyday lightweight sheer base so it doesn't have to match perfectly. I'm slightly too pale for it right now so I've been experimenting and mixing different base combinations to get my perfect shade.
A combo I've been loving has been the bareMinerals Complexion Rescue Tinted Hydrating Gel Cream in 7 and the Jouer Matte Moisture Tint in Nude. I love that both formulas are oil free! The bareMinerals base is very light weight but adds just the right about of darkness to my Jouer base that has a more medium matte coverage.
Do you mix your foundations?