Effect Of Different Colours On Blood Pressure Biology Essay

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This project was designed to determine the effect of different colours on blood pressure. A total of 24 subjects were required to look at specific colour for 2 minutes. Their respective blood pressure was measured respectively before and after each experiment. Time interval of 3 minutes after each measurement was set up to ensure blood pressure falls back to normal value before the next colour exposure. Friedman test was carried out to test the data and this led to the rejection of null hypothesis. To conclude, there was sufficient evidence from the statistical testing to suggest that different colours in our daily life can affect our blood pressure.


Colour is perceived by human eyes when different wavelengths composing white light are selectively interfered by matter.1c Humans can see colours due to the cones present mainly in the middle of our retina and a few on the periphery.1a Each eye contains six million cones with pigment that is sensitive to either red, green or blue.1b Sensation of light and visual sharpness are created through transmission of high levels of light intensity.1a Colour with wavelengths between that of primary colours stimulates a combination of cones. As a result, all colours can be detected in the visible spectrum which is about 400 to 700 nanometers.1b,1c One interesting fact about our eyes is that they can perceive more variations in warmer colours than cooler ones as almost two-third of the cones process the longer light wavelength.1a The picture below shows the respective wavelength each cone is sensitive to.



Both scientific and psychological effects of colour are suggested by many top scientists or researchers. The study of psychological effect of colour is defined as chromology.1d Maryland study by University of Loyola stated that colour increases brand recognition up to 80 percent.1g Improvement of readership, learning and comprehension with the help of colours is also noted.3a,3b Another interesting observation is recorded by Paul E. Boccumini, director of clinical services of San Bernardino County Probation Department in California. Children under detention are observed to cool down within 10 minutes after they are put in a room of bubble gum pink.4a Meanwhile, scientific application of colour in medical field is the usage of lights in full spectrum to cure depression for Seasonal Affective Disorder especially during winter months when the people are deprived of light.1e,2a

Hence, the ancient and once dishonoured field of chromotherapy is regenerated. Red is used to stimulate the body and increase circulation while yellow is thought to play a role in body purification. Blue soothes illness.1f

This experiment was carried out to investigate the true effect of colours on blood pressure and whether different colours affect us differently. If colours are found to really affect our body differently, then more attention should be put into colour consideration in fields such as marketing, education, art, and medicine. A person of high blood pressure should be more aware of the colour of their living and working environment. Colour surrounds us all the time. If we can fully understand and use it, it will undoubtedly influence and change our everyday life.

Statistical analysis showed that there is a significant difference in the effect of different colours on blood pressure. Red and yellow increases blood pressure, blue decreases blood pressure while green and black have fluctuated stabilising effect. This proved that it the effects of colours are biological and not merely due to psychological effect or experimental error.

From the table we could conclude that yellow showed greater increase in blood pressure with a higher mean and median of 11.54 and 10.50 respectively. However, it had results over a big range of data from minimum increase of +4 to a maximum increase of +29 and a highest standard deviation of 5.93 compared to other colour, which limited the creditability of the data. By plotting a box plot, we could determine that +29 is an outlier. Psychological effects that have been suggested for this colour are anger provoking and activeness.

Nevertheless, compared to yellow colour, a significant increase was also noted for red colour. But, red colour recorded shown a smaller range of data, and hence, smaller value of standard deviation, which made the data more reliable than the yellow colour. Furthermore, it was also interesting to note that the box plot of red colour was positively skewed with more people showing greater increase than the median. Red colour is more commonly associated with excitement and awareness of danger.

Blue colour, which is always linked to sadness and calmness, showed a neutral box plot with no skewing of data on the other hand. It was more concentrated with most people showed decrease between -3.00 and -7.00. Therefore, it could be concluded that blue decreases our blood pressure. The range of data is also smaller than that of yellow colour.

Green colour, a colour of stability, showed a positively screwed data of a mean of -0.17. Therefore, the effect of green is hard to be explained and might have slightly opposing effects under different circumstances. The differences and fluctuations of data could be due to cultural association and personal experience as well. Some fluctuation could be due to experimental error.

Last but not the least, three outliers were calculated for black colour. Though having a very small inter-quartile range, black colour portrayed the second largest standard deviation (5.52). Black is suggested to be a neutral colour. Yet, a few subjects displayed a very high increase of blood pressure when exposed to black colour. It could be due to sleepiness, or fear of dark environment.

Although the real scientific mechanisms of colours on our body are still undefined, but effects of colour are not directly psychological. This opinion was also voiced by Mr. Birren, an expert of colour. Alexander Schauss, a CEO and Senior Director of Natural and Medicinal Products Research at AIBMR Life Sciences, found interaction of colours in some unknown way with pituitary and pineal glands and hypothalamus deep in the brain which controls basic body functions and emotional responses. One or more brain neurotransmitter are affected by minute amount of electromagnetic energy according to Professor Harold Wahlfarth, president of Colour Science in German Academy and photo-biologist at the University of Alberta.4a Exposure to pure red light has been shown to stimulate the sympathetic branch of the autonomic nervous system. Pure blue light, on the other hand, lowers the heart rate, respiration, and blood pressure with special effect on the parasympathetic branch.2a 

In conclusion, colours can affect our blood pressure and different colours affect blood pressure differently.



Firstly, the subjects were of different cultural backgrounds and could have different life experiences that lead to change of mood and blood pressure when subjected to a certain colour which links to their past. Results obtained could be due to personal psychological effect instead of the pure biological effect of colour.

Furthermore, digital blood pressure monitor was used. Small fluctuations of data could occur and might be assumed to be change of blood pressure.

Besides, the subjects involved in this investigation were of small sample and involved merely college-aged students. It was not an exact representative of the true population of general-aged students. Limited availability of participants also occurred as the students tested were only from one college. Moreover, a human’s feelings are not controllable. Subjects might feel nervous or bored throughout the whole experiment even though a briefing was given beforehand.

Sources of error and ways to improve

The blood pressure might not be measured at exactly 2nd minute as there could be slight delay or increase of reaction time. In order to increase the validity and reliability of the result, reaction time is trained before the experiment. Second data cannot be taken as this will influence the time of measuring and also time of exposure to colours.

Blood pressure of normal humans also varied slightly throughout the day due to hunger, sleepiness and also a full meal. Therefore, all the experiments should be carried out within the period of 2p.m. to 5p.m. to prevent fluctuations of data.

Besides, the colour intensity exposed to the subjects might have varied a little bit due to the surrounding light although clothes were used. The environment could have changed throughout the experiments as not all the subjects data are collected in one day. Fluctuating weather, sunlight intensity, temperature and humidity all might influence the mood and feeling of subjects which indirectly affect the reliability of the experiment. Human are complex subjects. The experiment should be carried out in a constant air conditioned room with the same fluorescent light so that minimum changes of colour intensity can be achieved.

Further research

Study can also be done on the effect of colour on mood, stress, work performance and memory. As colour can affect our blood pressure, it might affect our daily mood and performance. Therefore, a good choice of colour in our surroundings can be made in order to achieve greater and better performance. A comparison between effects of colour on different gender can also be made as males and females have different anatomy. Hence, there could be interesting findings.


There is significant difference between the effects of different colours on blood pressure. Red colour and yellow colour increase blood pressure while blue colour decreases blood pressure. Green colour and black colour have fluctuating effects. Experimental hypothesis was accepted.


Sources 1 (b), (e), and (g) are all operated by educated professors. Source 1(e) is operated by Judie C. Snelson who is a Holistic Health Practitioner with a Master's Degree in Behavioural Science and a PHD in Religion. Source 1(g) is operated by Professor Jill Morton who gives seminars about colour and marketing, colour theory and everything that colour impacts. Lastly, Source 1(b) is established in 1997 by Professional Colour Therapist and Colour consultant- Valerie Logan-Clarke. Therefore, all the information of these sources is highly reliable.

On the other hand, Source 1(a), (c), (d), (f) and (h) are supported by big company and are very experienced. Source 1(a) is established by Pantone LLC, world-renowned authority on colour and provider of colour systems. It is a leading technology for the selection and accurate communication of colour across a variety of industries. Source 1(c) is funded in part by the U.S. Department of Education. Source 1(d) is based in UK and has been practising for over 10 years. Source 1(f) is a part of New York Times Company. Source 1(h) offers clear understanding of statistic’s basic learning. It is new with copyright 2010. All of this sites and companies are awarded and are ranked trustworthy.

Besides, newspapers, journals and books are all published. Therefore, they are definitely valid as sources of references. The authors are knowledgeable and are well-regarded. The newspapers and journals are peer-reviewed and have been cited by other people. Therefore, I feel that they are strongly valid as a choice of references.


1.1 top view of apparatus set up


1.2 subject was being experimented



2.1 Blood pressure monitor was attached and the blood pressure before the experiment was measured.