When you subtract colours of light, you will get a new colour or an absence of colour (black).

To work out what the new colour will be, you need to use the colour wheel here:

Here are two examples of this:

• Cyan light is made up of green and blue light. If you subtract blue light from cyan, you are left with green light
• Magenta light is made up of blue and red light, if you subtract red light from magenta, you are left with blue

As stated above, if you remove all colours from a source of light, you end up with no colours, which we perceive as black.