I have the Stila Perfecting Concealer and it is in the lightest shade. When I apply it to the blemish I blend well using circular patting motions with a concealer sponge or my fingertips or a concealer brush. When I am done and I set it, I can slightly see a little circle of color darker than my skin tone around the blemish. This isn't very noticeable, but slightly. Is this normal?

take a really little amount of it.

The final color result will depend on the kind of area you are concealing. If you are covering a red-ish zit, I would recommend using an even lighter shade. If that doesnt work, try using less.