color correction in fcpx
I second using Resolve, but there are a few "hidden" color tools you can access if you have Motion, or know someone who does.

Motion allows you to publish effects for use in FCPX and can be transferred from one machine to another. 

See this post from creativecow for a downloadable zip which includes 
Brightness,
Channel Mixer,
Color Balance,
Colorize,
Contrast,
Gamma, and
Hue/Saturation.

https://forums.creativecow.net/thread/344/14335