Sheep and Goats: Manipulating visual perception through colour relationships

Visual messages are hidden in plain sight through investigating the idea that artwork can be intentionally created to be experienced differently dependent on one’s visual abilities. The diptych Sheep and Goats both communicate unique details to individuals with the colour vision deficiencies (CVD) known collectively as colour blindness, and contain imagery visible only to people with typical colour vision. All the artwork is revealed to the different audiences through the use of digital devices fitted with augmented reality CVD simulation and recolouring software.

Each print in the un-editioned diptych is 84 x 112 cm. Through colour manipulation, each communicates different details to individuals with CVD than to those with typical colour vision. Chevrons dominate for those with CVD. Bull’s eyes dominate for people with typical colour vision.

The prints rely on circular imagery influenced by the Ishihara Test for Colour Deficiency and overprinted lyrics from Sheep Go to Heaven by the rock band Cake. The colour palette consists of red, magenta, blue and green tints. The imagery is layered with the repeated song lyrics typeset in Old Newspaper and screen printed in varnish. The bottom quarter of each print has the print’s title typeset in Old Newspaper. The paper is Somerset Velvet 255 g, printed with Ultra Chrome K3 inks using an Epson 9800 inkjet printer. TW Clear Gloss Base was double screen-printed through a T140 mesh for the lyrics.

Both the imagery and text were chosen because of their overt dichotomies; the Ishihara Test is a tool to identify one as colour sighted or colour blind. The Cake song, seemingly inspired by the Biblical parable in Matthew 25, declares “sheep go to heaven, goats go to hell (Cake, 1998).”

The lyrics of the Cake song are printed in clear varnish over the Ishihara imagery, and are intended to enforce the ideas of hidden messages and the dualist nature of the work by appearing and disappearing according to the position of the viewer and the light source.

The contrast of dualism against the inclusiveness of audiences and the mysteries of hidden messages was deliberate and harkens back to William Blake’s book, The Marriage of Heaven and Hell. Blake turns the dualistic Biblical proverb of the sheep and goats on its head by declaring that, “the lust of the goat is bounty of God” (Blake, 1790). In solidarity, dualism and the urge to classify and compartmentalize is opposed by Sheep and Goats through its diversity of audience perception and the revelations of the simulation software.

An understanding of how humans perceive colour underpins many of the techniques employed to develop these prints.

Human eyes perceive colour through three types of light receptor on the retina called cones. The three types of cone are distinguished by the wavelength of light that they respond optimally to; there are long wavelength, mid wavelength and short wavelength cones primarily detecting reds, greens and blues, respectively. When all three types of cone are functioning correctly we perceive the full spectrum of colours. If one set of cones does not function, colour perception is impacted and the range of visible colours is narrowed. In red/green CVD, either the medium wavelength cones or the long wavelength cones are dysfunctional and perception of reds and greens collapses along a blue/yellow axis, such that most reds and greens look like muddy yellow-browns. Colours like magenta look blue since the red in them is not perceptible.

This colour perception variation is used in the prints to create different visual experiences. Knowing how these two ways of perceived colour groupings interact with each other facilitated targeting of the different cohorts.

The colour and value contrasts that artists and designers use to help communicate visually are employed differently for the audiences. Artists know that the typically sighted tend to visually group warm colours (reds and magentas) and cool colours (blues and greens) separately. Thus, contrast for the typically sighted can be created using cool colours and warm colours. Those with red-green CVD exhibit different colour grouping preferences. They tend to group what those with normal sight view as red and green colours together because, to them, they all appear as muddy yellows. Similarly, blues and magentas are grouped together because they all appear blue. Colour contrasts for these audiences are most easily made using blues and yellows.

So, a pair of similar warm colours for the typically sighted is red and magenta. The contrasting cool colours are green and blue. For those with red-green CVD a pair of similar colours are blue and magenta, which appears blue. A pair that is visually contrasting to them are red and green, which both appear as yellow-browns.

This colour perception variation was used in the prints to create different visual experiences. Grouping the colours strategically allowed the creation of visual messages to one audience that were camouflaged to the other.

To ensure that the prints were experienced differently dependent on visual ability, the imagery was tested on a self-identified red-green CVD cohort. Of the eight volunteers, two knew their CVD diagnosis. Both had variations of red-green CVD. For the test, each was emailed a JPG of a work in development and asked “Can you let me know if you see any letters, numbers or patterns in the image?” Once an intended pattern was firmly identified by a significant portion of the test group, the test was considered successful and that variant would become the final image for the print. Because of the similarity of the colour schemes used in the prints, only one image required this testing process.

Tablets loaded with CVD simulation and recolouring software were used to see the artwork differently. For this, a tablet based application was created that both simulates CVD and recolours for those with CVD, allowing them to appreciate a wider range of colours for this investigation.

The CVD simulation software emulates the collapsing of the visual colour spectrum experienced by those with CVD. A digital image of the artwork is captured by a tablet’s camera and viewed in real time. The software identifies colours in the digital image, pixel by pixel, and substitutes those colours for the ones they collapse to on the blue/yellow axis.

The recolouring for CVD software also acts on images captured by a tablet’s camera. It rotates the red-green-blue (RGB) colour representation used by the device to green-blue-red. Consequently, red becomes green, green becomes blue and blue becomes red. For example, suppose an image contains red strawberries against green foliage. The recolouring tool maps the colour of the leaves and berries to a colour combination that is more differentiable for someone with CVD (i.e., red leaves and blue berries). This introduction of a false colouring scheme helps restore the perception of colour differences for people with CVD (Lyons and Flatla 2014).

Audience response

Sheep and Goats was exhibited as part of Generation, a Scotland wide Commonwealth celebration of contemporary visual art in 2015 and Print Festival Scotland in 2016. During its exhibition, audiences interacted with the art differently, as expected. The general tone of comments was that of enjoyment. The titles of the prints generated many positive comments as did the interaction spurred by the software.

Attendees with normal vision were first engaged by familiar imagery of the work and the changing surface texture resultant from the varnish printed text. When using the tablets containing the CVD simulation software the comments “this is very interesting” and “I never know things looked so different for the colour blind”, were noted.

For those in attendance with CVD, there was a sense of delight, particularly prevalent once they were prompted to ask others with typical colour sight to discuss what was seen in the prints, and then use the software on the tablets to translate their experiences between each other. One couple in particular became very engaged in the prints and the software/tablet translations, she of typical colour vision and he with CVD.  In conversation, it was learnt that their vision differences were of interest to them throughout their relationship. And, according to them, the exhibition had been a strong step towards an understanding of each other’s perceptual experiences.

In Conclusion

Through the use and understanding of colour, artistic principles and computer science applications, a diptych print was planned and executed that had specific elements apparent only to targeted audiences of specific visual abilities.

The words and images used in the art had a connection to the intent of the project and gave indications to the underlying purpose of their creation.

Tablets loaded with bespoke simulation and recolouring applications allowed sharing those elements with larger audiences. Using these devices, those with typical colour vision were able to perceive aspects of the work specifically designed to be visible only to those with CVD. And, using the same tablets, those with CVD were able to detect aspects of the artwork that would typically be hidden from them.

The ability to embed these multiple interpretations within the same pieces has been sufficiently satisfying, though not unworthy of future investigation, as has developing tools giving viewers an understanding of how others might see the work.

It is hoped the application of the techniques developed can be refined to create a diversity of imagery with applications beyond that which is presented here.


Blake, William. The Marriage of Heaven and Hell. Copy D, 1795

Cake, (1998) “Sheep Go To Heaven”, Prolong the Magic, Capricorn.

Colour Blind Awareness. 2017. Available from: [Accessed 24 May 2017].

Ishihara, S. (1917) Instructions. Test For Color-Blindness. Handaya, Tokyo: University of Press.

Lyons,D. and Flatla,D. (2014) Eye For An Eye, Electronic Visualisation and the Arts 25, 49-55.