How do we decide what colours we mix to achieve the required colour. Do we do it by instinct, a bit of this colour, a little of that ? Here are some tips to help you put a little more science into the art of colour mixing.
Don't Use More Than Three Colours in a Mixture. The more pigments you mix together, the muddier your colours will become. To keep your mixes looking fresh and clean use just two colours (You can add white if necessary). If you apply these simple techniques to your paint mixing, everyone will surely be impressed by your brush-work. Hey, you may even be able to quit your day job!
Use a Key Colour in all Mixes. Add a small amount of the same colour to all your mixes. For example, try adding a small amount of burnt umber to all your mixes. Take this approach across the whole painting and you'll create a painting with a keyed colour range. Each colour will therefore have a least a little in common with its neighbours and (hopefully) this will pull your painting together.
Use a Coloured Ground for your Painting. Before you start to paint, give your canvas a coat or a stain of another colour. This will affect your painting in two ways: Firstly, the underpainting will unify all the coloours you place on top. Secondly, as you add colours over the top, the colour underneath will inevitably show through and change the colour perceived by the viewer. For example, a light wash of viridian green and burnt sienna will give a dark leafy greenness to a forest scene.
Use a Limited Set of Colours. Try using a very limited palette of colours. Try using the earth colours (yellow ochre, olive green, venetian red, raw umber, burnt sienna, raw sienna) and maybe french ultramarine. You'll be amazed at the range of colours you can achieve, but just as importantly, the colours you mix will be more 'together'.
Use Complementary Colours Side-by-side. Complementary colours are 'opposite' colours. For example, the opposite or red is green, the opposite of blue is orange. Place two opposite colours next to each other on your canvas and the eye will perceive both colours as more intense. Don't just think of this phenomenon in terms of bright, primary colours, try it in subtle tints and shades. For example, I recently contrasted a pale blue shirt against a white background by adding a little cadmium orange to the white mixture. The effect was to 'lift' the blue shirt slightly and move it away from the very slightly orangey background.
Mix Complementary Colours to Make Darks. Mix cadmium red with pthalo green to get a colour that is very near to black, but twice as interesting. Add white to get a beautiful grey. Or try mixing ultramarine with burnt umber to give a fantastic dark that can be warm (add more umber) or cool (add more ultramarine).
Use a Lighter Tone to Separate Two Colour Areas. A trick used by some artists is to slightly lighten the of a colour at the border with another. For example, look closely at 'The Geographer' by Vermeer. At the edge of the blue gown Vermeer adds a little white to the colour of the distant wardrobe. This has the effect of intensifying the blue colour and putting distance between the figure and his background, opening up a three dimensional space the brings the nearby figure into sharper relief.
Use warm and cool colours to introduce depth. The mantra is "warm colours advance and cool colours recede". Its boring (and perhaps a cliché) but it does work!
Use complementary colours to model shapes. Rather than using shadow colours to suggest the gentle curve of someone's cheek in a portrait, mix a little ultramarine or viridian green into the flesh colour mix. The effect will be more subtle.
Practice Your Colour Mixes. Don't experiment with colour mixes on your best pictures, paint colour swatches instead. For example, mix pure ultramarine with pure viridian green and paint a stripe on a cheap, throwaway surface. Then add a little white to the mixture and paint another stripe next to the first. Gradually introduce more white into the mixture until the mixture is almost white.
Finally, Remember to Forget the Rules! Be prepared to forget everything you ever learnt about colours and colour mixing. Okay, so warm colours advance and cool colours recede? Try painting a sunset.