I mean that when you have a clip selected in the timeline, that you're thinking of applying an effect to, when you move your mouse over the effect (your color effects) in the effects browser, FCPX shows you a Preview - of that effect on your clip.
This preview only appears to be working on some of yours.
I'll make a list & post it here...
thanks
[EDIT]
Ok, with a clip selected in the timeline, running the mouse over your various effects, creates no discernible difference in the clip's appearance in all your effects except - Color Reduce a4d, Gradient Colorize a4d, & Open EXR Tone Map a4d, the latter just appears to darken it slightly. So, out of 11 Color Effects, the preview function only works in 3 of them. Hope that helps.