1. Both science and art teachers agree that red and blue are primary colors, but disagree on the third primary color, with science teachers saying it is green and art teachers saying it is yellow. 2. Color theory explains that the primary colors are actually magenta, yellow, and cyan when mixing pigments or inks, as these colors cannot be created by combining other colors. 3. The idea that the primary colors are red, yellow and blue likely originated from early mislabeling of colors and has been passed down through generations without being corrected.

1. W H E N P H Y S I C I S T S M E E T A R T I S T S
Author: Mr Lam

2. Primary colours
 Every science teacher tells students that the primary
colours are
 Green
 Blue
 Red
 Every arts teacher tells her students that the
primary colours are
 Yellow
 Blue
 Red

3. The science teacher says
 A science teacher will show you three lamps with
difference colours intersecting.
 Therefore, green, blue and red
 are the primary colours

4. What the art teacher says
 An art teacher will then get some colour pencils, oil
paints or crayons and show you this picture
This shows green can be
created by mixing yellow
and blue together.
Moreover, no matter how
hard you tried, there
seemed no way to
mix pigments
to create yellow. Therefore,
yellow is a primary colour.

5. Who is right, then?
 From the previous slides, both teachers agree that
red and blue are the primary colours. They have
discrepancy between yellow and green as one of the
primary colours.
 Before we answer this question, we need to go back
to the basic, understand some colour theory.

6. Why apple is red?

8. How about banana?
The answer is not that
simple.

9. Reflecting green-red or pure yellow?

10. Our eyes have three types of cone cells
 Red, green and blue**
 These cone cells response to different wavelengths
stimulations.

11.  The label for “red”, “green”
and “blue” cone cells are
quite misleading.
 They not just response to a
single wavelength but
rather a broad range of
wavelength.
 In the above figure, the
dotted line is the response
for rod cells
• Also notice how close
together the red and
green cones are in their
sensitivity.

12. Why we see orange colour?
We see orange colour because, both green and red cone cells are stimulated by the light source at the
same time. The ratio of the stimulations to the green cone cells and to red cone cells is resembled in
the brain and make us feel there is a orange colour. However, if we artificially adding any light within
the green and red cone response curve, and having the same ratio, we an recreate the sensation of
orange even we are really seeing the orange light!!
This is how
we see
colours!!!

13. As we have mentioned, magenta is composed of two
primary colours, (red and blue)
If a beam of magenta light laminates on a red filter,
only the red component can pass through.
The following slides show different colour beam rays
for different colour filters

15. Red light can pass through both yellow and
magenta filters

16. Red light cannot pass through a cyan filter

17. We can use different colour filters to subtract
colours

18. Colour reflection is actually is a colour filter.

19. The diagram below summarized colour
subtraction

20. Let’s go back to the original question
 What are the primary colours?
 By definition, primary colour can
 can be mixed with other primary colours to produce any other
colours.
 primary colour cannot be re-created by mixing of any other
colours by any ratio
 Actually I have already answered the questions from
the previous slides.

21. Primary colours for light (addition) is just opposite to the
primary colours for pigments (subtraction)
Primary colours of light
(addition)
Primary colours of pigments
(subtraction)
Primary colours: red, green blue Primary colours: Magenta, yellow,
cyan

22. cyan + yellow pigment = green pigment
Note: Cyan pigments look very much like blue when concentrated.

23. Wait a minute!
 You said the primary colours of pigment are:
magenta, yellow and cyan?
 How comes my teacher told me that the pigment
primary colours are red, yellow and blue?

24. Misconception over generations
 I am not sure why most art teachers (including mine)
claimed that primary colours were blue, red, yellow.
Perhaps, it was their teachers told them. The teacher’s
teacher told the teachers. and perhaps, someone had
made a mistake in the very beginning and pass from
generation to generations.
 My humble guess is that the first one probably
mislabelled red for magenta, and blue for cyan at the
beginning. Or “cyan” and “magenta” are not in the list of
the common vocabularies in our daily conversation.
Hence, they use “blue” and “red” instead.

25. Not convinced?
 By definition, a primary colour cannot be produced
by mixing from any colours with any ratio.
 If red were a primary colour for pigment, then it
would not be able to be created by mixing any
other colours.
 We can try to mix magenta + yellow and see if you
can produce red OR cyan + magenta for blue

26. Still not convinced?
Inkjet printers used
magenta, yellow and cyan
as their cartridges.

27.  From the inkjet cartridges, there are no red or blue
cartridges. Ask yourself, how can an inkjet printer
prints red and blue colours?
 It can’t be come from nowhere!!!

28. Conclusions
 The primary colours is red, blue and green.
 For practical uses for mixing pigments, secondary
colours, yellow, cyan and magenta are used to
produce other colours by subtraction.