You can bring up the Vectorscope Window by doing any of:
Opening up the window from the main toolbar's
W
button.
By using
RMB->Window->Vectorscope.
A Vectorscope is a tool used mainly in video productions as a debugging
aid. It basically shows you color information.
The display represents color in a circle or pie and each square
(R,M,B,C,G,Y) represents a pure primary or secondary color
according to the NTSC or PAL standards. No red, magenta,
blue,
cyan, green or yellow color is expected to be brighter/more saturated
than the squares (ie. go beyond them).
Each color of the color bars, for example, is expected to land
perfectly within each of the squares.
However, when dealing with computer graphics or bad video, it is
perfectly possible for a signal to create colors that are too bright or
saturated for the TV standards. If a color is too bright or
saturated, it might lead to problems in the broadcasting of the
transmission and may force the tv channel to have to desaturate all
your image.