Coloured filters absorb all other colours except for the one we see when we look at it

If you direct white light at a coloured filter, only the light that is the same colour as the filter gets through.

Here is an example of white light being directed at a green filter. You can see that only the green light has got through.

Here is an example of white light being directed at a red filter. You can see that only the red light gets through.

If you direct a single colour of light at a coloured filter which is a different colour to the light, it will not get through.

Here is an example where you direct red light at a blue filter, the red light is absorbed by the filter and none gets though.

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