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, and is used by black and white receivers. 

The colour signals are known as Er, Eg, and Eb.

The red and blue signals are converted into two new signals called the red and blue colour difference signals.
They are (Er - Ey) and (Eb - Ey).
These two signals are modulated onto a "sub carrier" at 4.43 MHz which becomes the chrominance (colour) signal.

The luminance, chrominance and sync signals are combined and are then used to amplitude modulate  a carrier in the UHF band.

An associated sound signal frequency modulates a second carrier, which is 6 MHz apart from the vision carrier.