Colour theory! There’s so much to learn about it. Usually, we think that it’s as simple as one colour mixing with another until, voila, you make a new one. It can begin to feel confusing when we start talking about RGB and CMYK colour models, mostly because the letters feel a little tough to understand at first. But, luckily, it’s not so different from regular colour mixing. Here we’ll break it down so that you can understand how colour theory changes depending on where it’s used. In this quick read, we’ll break down the differences between RGB and CMYK colours, oh and what that strange word ‘gamut’ means!
Not a fan of reading? No problem! We have a short and easy YouTube video all about RGB and CMYK colours that breaks down the concepts in more detail!
What are RGB Colours?
Before we get into the details of CMYK and RGB colour theory, it’s important that you understand what they are.
RGB stands for Red, Green, Blue. These are your primary colours of light. This means that if you shine together a red and a green light, they’d make yellow, a green light and a blue light would make cyan, and a blue light and a red light would make magenta. These are the secondary colours of light that are formed when one colour is mixed with another. If you add red, green and blue light together (all three primary colours) they combine to make white light. We see this in nature with rainbows, when white light disperses to create colours! RGB colours are used primarily on screens, like TVs, computers, phones, and stage lighting.
What are CMYK Colours?
CMYK stands for Cyan, Magenta, Yellow, and Black - K in this case stands for ‘Key’ which means black. You may have heard of CYMK in your printer cartridges because this colour model is primarily used for printing. These are different from the usual primary colours red, yellow, and blue (RYB) we think of because cyan, magenta, and yellow are the purest primary colours that are found in pigment. This means that if you mix together a magenta and a cyan pigment, they’d make a blue, a cyan and a yellow pigment would make green, and a yellow and a magenta pigment would make red. These new colours that are formed are the secondary colours of pigment.. When all three of the primary colours are combined, a dull black is made. Because of this, true black was introduced in printing processes since it is more efficient and darker than combining the three other pigments.
Additive and Subtractive Colours
Now that you know what RGB and CMYK colours are, it’s important that you learn what makes them so different from each other. CMYK and RGB colours fit into two categories: additive and subtractive. The RGB colour model are additive colours, or colours of light. This is because when they are mixed, they become lighter, or we can even say they ‘add’ light. On the other hand, CMYK and RYB colour models are subtractive. Different from RGB, colours of pigment lose or ‘subtract’ light when they are mixed, becoming darker.
Did you notice that the secondary colours of the additive colour model (cyan, magenta, yellow) are the same as the primary colours of the subtractive colour model? The secondary colours of the subtractive colour model (red, green, blue) are equal to the primary colours of the additive colour model!
The Primary Colours of Light - Additive Colour Model
The Primary colours of light are also known as the RGB colour model. These colours are used on screens, projectors, and stage lighting. They occur naturally in rainbows and when light shines through prisms! Have you ever noticed a rainbow of colours reflecting off of the furniture in your house when light shoots through a window? That’s additive light in action!
The Primary Colours of Pigment - Subtractive Colour Model
CMYK colours are used in pigment, also known as the subtractive colour model. Pigments are colours made from organic and inorganic physical compounds. This is what is used in acrylic paint, inks, markers, coloured pencils, and watercolour. When CMYK colours are mixed together, they become darker. We see this a lot when we paint. Imagine you’re painting a picture and don’t clean your brush in between colours. Your colours will mix and probably start to create darker or muddy colours. That’s because light is being subtracted from the colours, or in other words, getting darker in value.
What is Colour Gamut?
Now for the word that will sound really strange if you’ve never heard it before: gamut! Gamut is the spectrum of visible colours that are available to the naked eye. This means that our eyes can only see a sliver of the colours that actually exist in the physical world. Our naked eye can only see the colours of visible light, also known as the rainbow (aka ROYGBIV), but the actual spectrum of light extends far beyond what human eyes can see.
Some creatures, like butterflies and bees, can see UV light, and some snakes can see infrared light to help them hunt at night. Although there are so many colours outside of what we can see, the ones that we can see make up the colour gamut!
In the image above, the large yellow triangle is the RGB colour gamut. This refers to all of the colours that we are able to see from projected light (from a screen for example).
The smaller blue triangle shows the CMYK colour gamut. These are the colours we can see in pigments. Since the blue triangle is smaller, there are less colours that we can see in CMYK. This means that if we have a beautiful picture on a screen, the printed version of that picture will be in CMYK. This will give it a smaller colour range than it had when it was in RGB on the screen. Take a look at this image below to see what a RGB (screen) colour gamut would look like versus a CMYK (printed) colour gamut of the same image.
Major difference, right? The printout is a lot duller than the screen. This is because there’s no way for white to be printed as brightly as it appears on a screen.
RGB or CMYK: Which one is better for digital art?
Now that we’ve learned the differences between RGB and CMYK colours, which one is better for digital art? Since digital art is made using some form of technology, whether it is a computer or a tablet, that means that we need to choose the option that works best on screens. From what we learned above, we know that CMYK colours are best for pigments like painting and ink. This means that to figure out which is better for digital art, you need to decide where the digital art will be viewed. If the art is only going to be viewed on a screen (like animation) it should be done in an RGB colour space, since this works best on screens and has a wider range of colours. If you plan on printing the art, it’s best to work in CMYK so you have a true idea of the colour. Neon colours and other colours outside of the CMYK gamut can only be printed using spot colours (also known as PANTONE colours), but this process can be costly. Spot colours are pigments such as metallics, neon, or other super bright colours that cannot be made with CMYK alone. If you are creating digital art that will exist on BOTH screens and as physical prints, it’s better to work in RGB because the colour space can be easily converted to CMYK on most digital programs.
So, really, the decision is yours! Choose whichever option works best for where you intend for your art to be seen!
When to use CMYK vs RGB
Although RGB colours are best for digital art that is meant to stay digital, CMYK colours do serve a really important purpose. CMYK is great for painting pictures or printing posters. It’s necessary so that we can use colours in a physical sense. These are colours we can touch and can end up making a mess with if we’re not careful.
Try testing out colour theory by mixing CMYK colours! You can use markers, pencil crayons, or paint to see how these pigments mix and change. You can even see CYMK colours in action if you look at a printed brochure or the front cover of a book. If you want to experiment with RGB colours, test out digital art and the large array of colours offered through light technology! Or maybe take the time to stare at the next rainbow that crosses your path, because who doesn’t love to do that?
If you’d like to learn more about colour theory visit our All About Colour playlist that breaks down the different ways you can use colour in your art! Now that you’re on a colour theory roll, take a look at our related blog that discusses The Elements of Art - COLOUR.
For more classroom resources, visit our teacher pay teachers page for worksheets and lesson plans for your classroom! You can also check out our art resources for teachers page, where we cover all of the elements of art.
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