What is already in FCP X is miles ahead of what FCP 7 can do.
Not in my opinion.
The "color board" in FCP X is an unnecessary move away from the standard color wheel.
Color adjustments in FCP X are spread out over three tabs where as in FCP 7 they were in a single window.
The "color mask" in FCP X (aka "limit effect" in the 3-way Color Corrector) is very limited compared to the old 3-way CC. In FCP X you can select a color but then only have a single "less/more effect" slider for adjustments. In the 3-way CC you can select a color then adjust the hue, saturation, luma, edge enhancement and softness to really dial in exactly what you wanted.
The 3-way CC let you use an eyedropper to set your black level and your white level. And when you used them the settings in the 3-way CC actually changed so you could see what the filter was doing.
The auto correct and color match in FCP X are okay if the footage is already in good shape but they are all or nothing filters. Their changes don't show up in the CC filter so there is no way to tweak the results other than adding another CC filter and making changes by hand. But if you knew how to fix it by hand you probably wouldn't have had FCP X auto-fix it to begin with.
The CC filters in FCP X can't be reordered like they can in FCP 7.
The speed in FCP X is much better and being able to apply the shape mask is very handy. I wish you could tell it if you wanted to work inside the mask or outside the mask though.
While they are certainly improvements in the CC filter in FCP X I think it's a net loss compared to the 3-way CC filter in FCP 7, IMO.
Lethal