Color Grading Central
Color Grading Central has a mix of free and subscription based tutorials on color grading using FCPX, MBL2 and of course DaVinci Resolve.
I found the site when looking to become more proficient at color correction and ultimately, to be as good as anyone I could hire to do the same task. Denver Riddle, the site owner, puts out professional tutorials with an upbeat attitude. Check out some of the free Final Cut Pro X tutorials on Vimeo.