
If a picture looks too red, it is considered too 'warm', this is because colours like red, yellow and orange are associated with summer and warmth. An example of a picture being too 'warm' is to the right.
This is an example of a warm image, notice how the levels of red on the bottom half of the screen take dominance. This means that more red is being put into the image, and more green and blue is being taken out.
There are still signs of blue and green levels in there, but you can notice which colour has taken priority in this shot when changed to be like this.
This is an example of a cold image, take note on how the picture contains a lot of blue colour and tint. This shows that there is mostly blue in this image. There are still some bits of red and green, but they're pretty much consumed by the colour blue.
So why do we need pictures to be not too warm but not too cold? Well the picture itself, when balanced out in red, green and blue, it makes it so that the picture is much more clearer and easier to look at, it looks like it's taken there and then.
Pictures can turn too warm or too cold due to lighting, natural and unnatural lighting are the factors of this.
The reason four colours were mentioned, is that they are four of the most common colours you'll come across when correcting colours like red, green and blue. When you take out red, you get levels of blue increasing the more you take out of red. It's also the same vice-versa, when you take out blue, red ends up increasing.
The other two colours, magenta and green, are the same for this, in fact they're the exact same, when you extract levels of magenta, then the colour green starts to seep in, and vice-versa.
The picture to the right is s hot of the effects control tab, to which this is the tool you use to change the levels of red, green and blue in the clip you've selected. You can adjust what colours and shades of a colour you can set for the shot, it's a way of equalising the shot if it's too warm or too cold.
This shot here is an example of a relatively balanced out shot when it comes to RGB colour correction. The levels of red green and blue are almost on par with each other and they've resulted in a cleaner picture that doesn't look 'off' in colour.


