Read the pages on the monochrome camera, and light and colour.
Note that this page describes the UK colour system (PAL).  Light
enters via the lens on the left and is split into three paths by
mirrors and semi-transparent mirrors.  The light in each path
passes through a colour filter. These filters are like the
transparent coloured papers in which chocolates are wrapped. If
you look through a red one, everything looks red. This is
because it lets only red light through. Blue or green objects
look black. Colours which contain some red, such as purple, look
dark red. Red, blue and green filters are used.  The coloured
images are focussed on the faces of the three colour tubes which
scan the images. Each tube gives a signal out, proportional to
the amount of colour.  Some of the red, green and blue signals
from the camera tubes are added in the luminance matrix. This
means that the separated colours are recombined electronically.
This gives a luminance (brightness) signal. The luminance signal
is labelled Ey,