I have loved one particular color of lipstick for years but it's just simply too dark for me so I take the lipstick out of the tube and place it in an empty Carmex lip balm container (other lip balm containers will work too but I happen to like the glass container. ;-) Then, in very small increments, add a much lighter shade from the same color scheme and microwave to melt. Do not do this with the lid on and be sure to check the melting every couple of seconds. Once melted, stir and test on your lips with a cotton swab until happy with the shade :-)
If you have a tube of 'almost empty' or even 'not happy with the shade' full tubes why not have fun and experiment ;-) You can also use the plastic daily pill cases and contact lens cases to make and store your new lipstick colors.
You'll feel like an artist at work and not be wasting money already spent.
Source: I learned this tip when I was a hairstylist at CBS TV, a couple of decades ago from the makeup artists I worked with. They had to color coordinate skin color, hair color and costume colors. Sometimes the standard lipstick colors just weren't quite right and they had to be clever on the spot.
By Deeli from Richland, WA