Whether an artist is specialising in pet portraits, landscapes, or traditional portraits, keeping colours as bright as possible is an important part of producing paintings that appear fresh an clean.
The appearance of any colour is dependant on the circumstance in which it is seen. The way a colour is seen is effected by the colours next to it and on which it is placed. For instance, yellow will seem washed out and pale next to white, but strong and bright next to black. Colour also has tone and can be put into groups. Lemon yellows, golden yellows, oranges and yellow earth colours can be subsituted for one another in mixtures or used to shade each other when describing form. Also, many colours will have an undertone, meaning that they have an element of another colour in their make-up. For instance, red may range from having pronounced yellow undertones to blue.
Laying out your palette
Firstly, the artist should always consider the permanence of his or her colours and limit these to as few as possible, try to avoid colours that are very similar. Laying out your palette properly is important, as it'll make the whole painting process easier. Messy palettes, where colours contaminate each other, muddying their appearance and hence, the appearance of the painting. For complicated techniques, that involve several stages, it's best to lay out a selection of palettes representing each stage of the process. The aim is to have colours placed far enough away from each other so that they do not get contaminated plus, the area where you mix these colours, should also be kept away from the original colours so that you keep them as bright as possible. Best practice for colour placement, is to put them in a line in order of importance along the top of the palette, so that the most used colours are within easy reach. White is ordinarily placed nearest the thumb (in the 'top' spot as it were), but some artists like to have the white in the centre of the line. If particular colour mixes or shades are anticipated, these can be laid out in lines under the main colours.
The permanence of colour is decreased when mixed, a few colours can become very impermanent if diluted too much. Indeed, when mixing colours, you should keep the amount used to just two or three, this will avoid colours getting too muddy. All the same, you need to be aware that many commercial colours are already a mix of different pigments, so will be more likely to produce muddy colours if over mixed. Brighter tones can be achieved without the loss of colour saturation by mixing with sympathetic colours.