Since all scopes operate on the image they see in the preview window within Premiere Pro, we can use a mask or a garbage matte to mask out an area of the video that should be perfectly white. For example, we could mask out a section of a white shirt. The RGB parade and vectorscope will update automatically to show the colour information for only the masked out area.
Note that we would expect the shirt to be pure white. However, the RGB parade shows that there is a clear magenta tint in the image because the red channel is strongest, then blue and then green. In a properly white balanced image we would expect the pixel distributions for all three channels to lie on the exact same line.
The same holds true for the vectorscope. We can clearly see that the pixels in our video are distributed towards magenta. In a perfectly white balanced image we would expect all points on the vectorscope to be exactly centred to indicate that there is no colour in the image. We can clearly see that the pixels in the image have a magenta tint.
To fix the white balance, we can again use a Curves effect. We can bring down the red, lower the blue and slightly raise the green channel. This will level out the RGB parade and bring the vectorscope back to the centre.
The shirt in our video is now correctly white balanced. Both the RGB parade and the vectorscope show the expected pattern for an image that contains no colour; the RGB parade is balanced and all pixels in the vectorscope are centred.
If we remove the mask we can see that the final image has been properly colour corrected.
Finally, whenever colour correcting a video with a person in it, it is advisable to check that the skin tones are correctly represented. For this we can use the vectorscope. Independent of skin colour, when you mask out a section of a person's skin, the saturation pattern you will see is always the same due to the blood that runs underneath the skin. The following image shows the analysis of a video with only a section of the person's skin masked out.
For properly colour corrected skin, the RGB parade should show the red channel as the strongest, then followed by green and then by blue. More importantly, in the vectorscope, all the colours should fall onto the line between red and yellow. This line is called the 'Skin Tone Line'.
You can use all sorts of different colour correction effects like the Curves or the Fast Colour Corrector in Premiere Pro to make sure your skin colours fall onto the skin tone line. This will ensure that your skin colours are correctly represented in your video.
Colour correction is a real art form and it can be difficult to get the colours right depending on the contents of your shot. With a good understanding of the tools available and some practice you can ensure that your video will look a lot more professional no matter what device it is played back on.