Colour of the transition metal complexes
Most colour in chemistry comes from selective absorption of light by electronic transitions of the appropriate energy

Colour is not limited to transition metal complexes. They have a particularly rich range of colours as the electronic transitions often match the energy range of visible light but also because they are easily altered by the nature of the ligands surrounding the metal (for example, Cobalt complexes can be almost any colour of the spectrum depending on the ligand).

But plenty of other compounds are coloured. Most dyes are purely organic and the colour comes from the absorption of light in transitions between molecular orbitals made from unsaturated chains in the molecules. Many elements are coloured because they, too, have some electronic transmission that matches the energy in some part of visible light. The mechanism for colour is the same in all these cases.

There are other ways to generate colour but they are less common. Some colours come from interference not selective absorption of light: some physical structures that contain features close to the wavelength of light  can reflect light but in a way that causes selective interference that cuts out some colours. This is why oil films on water produce rainbow colours but is also the source of unusual colours in some fruits, butterflies and birds.

Are things coloured if the light isn't present? That is a philosophical question like "does a tree falling the the forest make a sound if nobody hears it". From a chemical point of view the feature that creates colour is still present whether or not there is light. But in the absence of light nobody is going to notice it.