I love mixing lipstick colors, It give you control of the shade you want to end up with, the finish and can "fix" the a lipshade that was too light or too dark for you.
I first started to do it when I go "Tribalist" from the MAC "Style Worrior" collection. That shade looked ok at the MAC counter and the sales lady sold it hard to so I bought it. Once home I tried it and really didn't like how dark it actually was. But I absolutely love the purple in it. So I tried it on with MAC's "Fresh Brew" which I found too light for me and ended up with a beautiful lighter redish purple.
[This was from when I was sick a few weeks ago and was bored out of my mind and decide to play around with my makeup- The lips on this pictures are a mix of the colors mentioned above]I just love mixing my lipsticks, I don't think I can go back to a single shade on my lips or worse a single product! The lipstick I use the most to mix any other color is "Taupe" or "Verve" from MAC to darken or "Fresh Brew" to lighten.
I also like to mix lipsticks with pigments.
[Here again I was ill and just started playing around with makeup. I love my lips here. They are a mix between "Sunsational" from Mac and BarryM dazzle dust in "Tan"- It gives it that beautiful slivery gold shade]
I think I'll introduce a mix of the week... I'll think about it
All this to say MIX YOU LIPSTICKS!!!
There is an infinite possibilities of combinations and colors you could end up with just experiment and document :D