Part 3 : Colours of objects
Every object has a colour, and can be defined by one. But we have to understand how the object is affected by shadows and surroundings. To make it visible enough let's take a pool ball. When you cast a light on it - you can see that the colour of it is not plain, it has local (true) colour, colour close with tone and surrounding colours (reflection) and specular highlight.
(1 - specular highlight, 2 - local colour, 3 - reflections, 4 - colour close with tone)
As you can see, the red ball is full of tones. But if you remember the rules of colour interaction - it will be easy for you to rule the colour. The rule of a thumb - most generally we paint shadows by adding black and red to local colour, while adding yellow/green and white to the highlights. This makes nice, deep shadows and bright, live highlights. This situation changes whenever you feel like it - the lighting can get blue, red or of any other colour, affecting the whole scene. The shadows can be cold - blue and lighting can be live and yellow (as on the photos on the bottom). But remember - never make shadows with just adding black to it - it will look ... dirty. I'll prove that later on.
Another thing is the strength of the light. Objects that are lighted with it - especially red and yellow - are well saturated and reflect it very strongly.
When the light is fainter - all the objects get desaturated and blue.
(photos taken from H.Parramon book of colour theory)
When the atmosphere gets in a way, different situation takes place... The further the planes get from the observer, the more blue and less contrasted they are. It is especially well seen on the landscape photos:
There are also other factors like fog, clouds, smoke etc. that affect the scene.
Part 4 - Contrasts
Comparing to nature our colours are very poor. Imagine a situation - there is a hole in a wall, that leads to a dark room. There is literally no light in it. Then, next to the hole we hang a black sheet of paper. When we compare them - the paper is really dark grey in contrast to the hole.
So we have to immitate the colours by playing with contrasts. The general rule says, that the colour seems brighter, when the surrounding colour is darker. And the opposite - the colour seems darker, when the surrounding colour is brighter.
The same colours of different values put together strenghten each other: