Mixing colours digitally is not the same as mixing them physically – we explain what the difference is and how to go about it in practice.
Mixing colours to form hues and tints is a fundamental skill for every artist and designer, but there’s a difference between mixing in traditional media and digital paint.
In our formative years at school, most of us were taught how to mix three primary colours together to achieve others on the colour wheel. That the combination of blue and yellow poster paint generates a green, while blue and red create purple.
By mixing red, yellow and blue in varying amounts, a wide range of colours can be produced. However, mixing colour digitally works differently, and one of the most challenging aspects of creating digital art is learning how computers produce different colours.
The additive colour model
Screens use an additive colour model rather than the reflective model you learnt at school, so instead of the primary colours comprising Cyan (C), Magenta (M) and Yellow (Y) – which are the pure version of the blue, red and yellow you were taught at school – the additive primary colours are Red (R), Green (G) and Blue (B).
(If you need further explanation of why there are two different models used to create colour, check out this article on colour theory.)
The idea of mixing together different amounts of red, green and blue to achieve any colour and tint is quite simple in principle, but it takes some practice before you’ll understand what to expect when you start painting with just those three colours.
How to make your own colour wheel
The very best way to get to grips with digital colour mixing is to experience the effects of different combinations yourself. Follow these simple steps to create a rough colour wheel, and learn how different mixes create different colours.
Step 01
Start by creating a blank document in Photoshop, or your preferred digital painting software. Set your brush to 100% opacity, and to use the Lighten colour blending mode.
Fill the canvas with black, and set your brush to use 100% red, 0% green and 0% blue. Paint a blob of this colour at the top of an imaginary triangle.
Change your brush colour to use 0% red, 100% green and 0% blue. Paint a second blob on the left apex of the triangle.
Finally, set your brush to use 0% red, 0% green and 100% blue. Paint a blob on the right apex of the triangle.
Step 02
Repeat the process, placing overlapping blobs of paint at the midpoint between the red and green points, in both red and green.
Do the same for the mid-point between red and blue, but painting with red and blue instead of red and green.
Finally, place a final pair of blobs between green and blue, using green and blue paint.
You should see the two sets of colours mixing to create yellow between red and green, cyan between green and blue, and magenta between blue and red.
Step 03
Paint a series of secondary blobs at the mid-point between your pure mixed colours, and the original apex points. Use 100% opacity for the colour closest to the point, and 50% opacity for the other colour on that side of the triangle.
For example, in between the yellow and red blobs, place a blob of red paint at 100% opacity, and overlay a blob of green paint at 50% opacity. Repeat for the remaining five spaces between the mixed and pure colours.
Paint a pure 100% version of each colour, overlapping in the centre of your triangle to see the effect of mixing all three colours together.
Creating different tints
Additive colour works so that the more light you add, the brighter the colour becomes. Mixing 100% opacity of red, green and blue together provides white, whereas mixing 0% of the three colours provides black.
It follows, then, that mixing 50% of each colour will give you a mid-grey. Similarly, if you want a dark magenta, you’d mix perhaps 50% red with 50% blue, or 25% of each to achieve an even darker version.
These different brightness values are referred to as ‘tints’ or ‘shades’ of the pure colour.
Colour mixing tools
Web design formats
Once you’ve got a good grip on how the three principal colours in the additive model mix together, you’ll be able to make educated guesses at what colours notated in common web design formats such as hexadecimal and rgba are likely to be.
So, for example it will become second nature that #ffff00 is yellow, while rgba(127,255,0,1) is a fully opaque lime green.
Colour mixing tools
Understanding the basic principles of mixing colours in the additive colour model isn’t the be-all and end-all of digital colour mixing. There are many colour mixing tools available to help make good colour combination choices – here are a few…
Adobe Kuler
Perhaps the best-known colour scheme tool on the web, Kuler allows you to generate an entire colour scheme from a single base colour, upload a photo to extract colours from it, and store/share your colour schemes for later use. It even offers direct integration with the Creative Suite apps and downloadable palettes for sharing.
Colors on the Web
Colors on the Web accepts a single colour in hexadecimal or RGB, and outputs a set of schemes based on different mathematical equations, similar to Kuler. This won’t work on iPad or iPhone though as it uses Flash to power the schemer.
ColoRotate
Offering similar functionality to Kuler, but with a nice 3D visualisation of the colour wheels, and the ability to generate more than five colours in a single scheme, ColoRotate can also be integrated directly into some Creative Suite applications, and offers a nice alternative to Adobe’s own offering.
Toucan
Part of the Aviary suite of online tools, Toucan allows you to create palettes with up to 20 different colours, using the same core set of equations as you’ll find in all the tools here. Again this is powered by Flash, so not available on HTML5 devices such as the iPad.
Software developers are also creating their own approaches to providing intuitive colour mixing on digital devices. For instance, Paper for iPad, by developers FiftyThree, recently received an update that allows users to buy their new colour mixing tool.
This uses a custom-built colour mixing algorithm that doesn’t rely on the traditional RGB model, but instead plots natural colour mixes based on that original understanding you got at school – so that mixing yellow and blue provides a complementary green.
This colour mixing approach was inspired by the work of a German study from the 1930s that split colour into six different dimensions, including reflectivity and absorption. By adapting the work of the two scientists behind the study, Kubelka and Munk, and conducting extensive user testing, the team at FiftyThree came up with a natural-feeling, intuitive colour mixing palette. Their work was enough to convince Apple to feature the app when launching iPad mini.
Words: Sam Hampton-Smith