Old fashioned color grading with SC Color Grade. Choose the color to "balance" a color cast, or use this to create moods. Uses the System Color Picker to provide an easy reference for balancing a color cast and to adjust "shadows" with the brightness slider. Use the Base Value parameter to adjust highlights. Both controls "massage" the midtones. Use a Color Mask to taper the effect over a luma range. This is a *simple* and powerful color tool.
I invented a way to create effects inside FCPX — build what you need when you need it without going outside FCPX. Highlighter 2 is a collection of bits and pieces of effects that can be applied to any content to create your own custom effects in Final Cut.