I have a 20w Induction CFL from Sylvania and for some reason the color shifts on it and is real noticeable. Starts out at about 2600K then goes to 3500K then settles out at around 2900K. What is causing this?

Probably old age, what position are you running it at?

It is a month old and is being run base up.

And what is the rated color temperature?
Lot of lamps do not have declared light properties immediately when new, but need some hours to settle (lamp's rating is valid for 100hours "age").
So if the rating was "3000K", then it is normal.
What is happening? Different components are settling their correct position and compound composition in the lamp. Exact details are really dependent on the exact composition and design of the particular lamp and this is often an industrial secret (phosphor or atmosphere fill composition at least) of particular manufacturer, so you will not learn more then the "generic" part...
This settling is often position dependent, so if you change the position, it might to start "playing colors" again, till it adopt to the new one. So do not move with the lamp...