There is no shortage of free additions for FCPX. One of the best I have come across so far has been a TON of preset color grades. These were created by Brendan Gibbons who has created so many useful plug ins and templates for FCPX.
What I love about all of these color grading presets is that if you go through your project and balance your color in color correction one, it is extremely easy to go through and add a look by adding the preset into a second color correction. And even add a different look in correction 3 and toggle them back and forth. Also, you can always tweak the preset to get exactly the look you want.
Currently he has three color grading presets.
I have noticed that having all of these installed at the same time makes the preset window take an extra second to open.
Oh and did I mention they’re low in sugar?