I'm a fairly smart guy.
Why is this happening?
I pull up 3 way color corrector and fiddle with the settings in visual mode....and nothing happens in the tool bench! V-split, H-split, swap.....no preview. Just original frames.
What the hell am I missing?
Did you highlight the clip before selecting the filter (or drag the filter onto the clip)?
Have you double clicked the clip with the filter to load it into the viewer?
If not, you are twiddling with a filter that is not linked to your clip. Also be sure to put the play head over the clip you want to adjust in order to see the results in the Canvas.