# The RGB Color Model

We live in a world in which **colours** play an important role – and that’s nothing new. Goethe considered his 1810 work on colour (‘Theory of Colours’) to be more significant than his literary works for example. And in 1809, British ophthalmologist and physicist Thomas Young (1773–1829) put forward the theory that all the spectral colours could be produced by combining three primary colours. However, there was no talk of RGB at this point. Young’s claim was only proved 50 years later, by Scottish scientist James Clerk Maxwell (1831–1879). Maxwell produced the first colour photograph in 1861 and is credited with proving the theory of **additive colour mixing**.

Definition RGB: The term RGB refers to a colour space that reproduces the colours visible to the human eye by mixing the three primary colours: **r**ed, **g**reen, and **b**lue.

**Colours** give **signals**, make things appear a certain way, and **appeal to the senses**. Strictly speaking, that’s exactly what colour is – a sensory impression of the light that we can see. It is electromagnetic radiation with a **wavelength ranging from 380 nanometres (purple) to 760 nanometres (red)**. As various image representation technologies have developed, so have several models for the optical representation of colours. With the emergence of colour screens, the RGB colour model has played a key role in how images are reproduced on electronic output devices. This guide covers all the most important information about RGB colours.

## How does the RGB colour model work?

The RGB colour space uses the three **basic colours** that the light-sensitive cones in our eyes react most to – **red**, **green,** and **blue**. The basis of this colour system is black. All the colours are seen in contrast with black. The term **additive colour mixing** comes from the fact that every RGB colour is made by combining – or **adding together** – the three basic colours. On a computer screen, individual dots (pixels) are displayed alongside one another to form an image. Each pixel consists of three sub-pixels (one red, one green, and one blue), which our eyes mix so that we see a single colour.

## How many colours are there in the RGB colour space?

Each of the primary colours or ‘**colour channels**’ as they are also known (red, green, and blue) can be assigned a value from 0 to 255, so there are 256 possible values for each channel. To find the total number of possible colours, we multiply together the number of colours available in each channel. This gives us 2563, or 16,777,216, which is why people often say there are 16.7 million colours.

[![Image: RGB colours and additive colour mixing](https://www.ionos.co.uk/digitalguide/fileadmin/_processed_/9/5/csm_rgb-colours-and-additive-colour-mixing_7e22da099b.webp "RGB colours and additive colour mixing")](https://www.ionos.co.uk/digitalguide/fileadmin/DigitalGuide/Screenshots_2021/rgb-colours-and-additive-colour-mixing.png) RGB colours and additive colour mixing On the **internet**, all these colours can be expressed using **hexadecimal** codes as well as **RGB values**. In fact, Cascading Style Sheets (CSS) often use both systems to ensure that colours are displayed correctly in different browsers.

```none
// Paragraph with text in fuchsia
p.colour {
	colour: #FF00FF;
colour: rgb (255,0,255);
}
```

This code snippet shows how **RGB colours are used online**. Several colours have **defined names** for use on the web and in CSS (for example, #FF00FF is fuchsia). You will find plenty of tables and lists of these colours online.

[![Image: RGB colours and the colour space](https://www.ionos.co.uk/digitalguide/fileadmin/_processed_/8/3/csm_rgb-colours-and-the-colour-space_bf5a8b9ef7.webp "RGB colours and the colour space")](https://www.ionos.co.uk/digitalguide/fileadmin/DigitalGuide/Screenshots_2021/rgb-colours-and-the-colour-space.png) RGB colours and the colour space The [graphics formats](https://www.ionos.co.uk/digitalguide/websites/web-design/graphic-file-formats-which-formats-are-important/ "Graphic file formats: which formats are important?") used to display images and graphics **online** are all based on RGB colours, except GIF. Image editing software like Photoshop and free [image editing programs](https://www.ionos.co.uk/digitalguide/websites/web-design/photo-editing-software-testing-free-tools/ "Photo editing software: testing free tools") also have an RGB mode to display colours. And [image compression tools](https://www.ionos.co.uk/digitalguide/websites/web-design/compress-images-with-the-help-of-free-tools/ "Compress images with the help of free tools") use RGB when compressing images for websites to boost performance.

Tip RGB or CMYK? Modern screens of all types and sizes use the **RGB** colour model for colour reproduction. The [CMYK colours](https://www.ionos.co.uk/digitalguide/websites/web-design/cmyk-colours/ "CMYK colours") on the other hand are used for colour printing.

## RGB, CMYK… anything else?

Of course! There are many different **colour space** concepts. Each reproduces colours in a slightly different way. Alternative colour spaces include:

### CIE 1931

**CIE** is the standard valance system created in 1931 using average values for standard observers. **CIE 1964** considers the field of view of the human eye, which is equivalent to an A4 sheet of paper seen from a distance of 30 cm. Other colour spaces were later derived from this (CIELUC, CIELAB and CIEUVW).

### RGB with extras

The **sRGB** colour space is a modified version of the RGB colour space, developed by several companies especially for the internet. It is used in open-source programs and for the SVG image format. Adobe designed a colour space called **Adobe RGB** to reproduce the colours of a CMYK printer on a computer screen. There are a great number of RGB colour spaces out there, each designed with specific display purposes in mind. In fact, anyone with the right skills can create their very own colour space.

### Hue and saturation

The **HSV** (also known as **HSB**) colour space describes colours by their hue (H), saturation (S) and brightness value (V or B). It is closer to how the human eye perceives colour. There are two other similar colour spaces: **HSL** and **HSI**. Here, the L stands for ‘lightness’ and the I stands for ‘intensity’. **HSL** can be used in **CSS**.

```none
// Paragraph with text in red
p.red {
	color: hsl(0, 100%, 50%);
}
```

### Luminance and chrominance

This type of colour space is used for colour television standards such as NTSC, PAL and SECAM. Examples include **YIQ**, **YUV**, **YDbDr**, **YPbPr** and **YCbCr**. They combine two colour values with one brightness value. There is also a newer, extended colour space for digital video signals called **xvYCC**.


This is a markdown version of: [https://www.ionos.co.uk/digitalguide/websites/web-design/rgb-colour/](https://www.ionos.co.uk/digitalguide/websites/web-design/rgb-colour/) for AI/LLM consumption.