The YUV curve lets you take an image and drastically change the look. The bottom half of this image shows how under-exposed the original shot was - the top have has been tweaked using the YUV curve. The line represents the brightness of the image with the point in the bottom left been black, and the point in the top right as white. By putting points along the line and dragging up we have increased the brightness of the midtones whilst not killing the bright areas, and by adding points near the bottom we can also crush the blacks to add a bit more definition.
This shot also started life too blue - but that was corrected by the 3 way colour corrector above and we are using these two filters together.
Notice the handy SAFE COLOUR tick box to make sure you do not change the image into areas you should not go!
This filter is called the YUV curve because it adjusts the Y levels (brightness) plus U (blue & yellow) and V (red and cyan). This picture does not show the U and V graphics and to be honest we use the 3 way colour corrector to sort out colour as we can generally get the results we want with a couple of clicks.