1. Colors are the smiles of Nature
Leigh Hunt

2. Introduction Color. Or is it?
How beautiful the world is because of color!
So easy to understand.
It’s one of the first concepts children learn.
It’s real.
It’s universal.
Or is it?
It’s not simple.
It’s not real.
It’s not universal.

3. Color wheels for mixing paint.

4. But why should a color wheel work? The spectrum is linear!
575 nm
400 nm
450 nm
520 nm
700 nm
Newton’s “color wheel”

5. Color wheels for mixing paint to neutralize color: OK.
yellow
green
red
cyan
Not OK for assigning visual complement in
spectroscopic analysis of compounds !!
magenta
blue

6. cosmic gamma X-rays UV Vis IR Radio induction power
Color is our brain’s response to light.
“Light” is a term that refers to a electromagnetic radiation.
And electromagnetic radiation are waves of different energies that extend over a broad range:
frequency, Hz Hz
cosmic gamma X-rays UV Vis IR Radio induction power
wavelength, nm nm
If the electromagnetic spectrum were a piano keyboard…..
the visible spectral region would be just one key!

7. Each of the “colors” of visible light has a corresponding wavelength
between 400 to 700 nanometers (or nm).
565 nm
Light having a wavelength of near 565 nm will look yellow to most people.
500
600
700
750
650
550
450
400
Is this because the eye has a specific detector (or receptor) for 565 nm yellow light?
And a different receptor for 450 nm blue light? And another one for 650 red-orange light?
And so on, for every wavelength between 400 and 700 nm?
Seems like that would be a LOT of different types of receptors.
Nature is “smarter” —and more efficient—than that.
Only three different receptors for visible light are used.

8. Beauty in the eye of the beholder.1
Your eyes have only three color receptors (detectors)
- the RGB cones (red-green-blue)
It is the brain that interprets visible light as “having” color.

9. Beauty in the eye of the beholder.2
Yellow light is perceived by our eyes when two color receptors, Red and Green,
are stimulated simultaneously.
This is indicated on the diagram by the red and green arrows.
It is the brain that interprets yellow light as “having” a yellow color.

10. stimulate the Red and Green receptors. See?”
Beauty in the eye of the beholder.3
“What about red-orange?”, you say. “Red-orange light would also simultaneously
stimulate the Red and Green receptors. See?”
Aaahhh…..true. But look! The relative lengths of the arrows are different.
The green arrow, i.e. G-receptor, is much less stimulated than the R -receptor.
So, red-orange light is seen as different from yellow light due to
the ratio of R and G response.

11. It is the brain that interprets color.
Beauty in the eye of the beholder.4
When the R receptor gets about the same signal as the G receptor, or R = G,
yellow is perceived.
When the R receptor gets a larger response the the G receptor,
something like R = 3G, red-orange is perceived.
It is the brain that interprets color.

13. THIS IS NOT YELLOW
Magenta is not a real color.
Biology
Philosophy

14. Magenta is a
non-spectral
hue.

15. Maxwell’s Triangle This triangle was devised to illustrate how
three primary colors —Red, Green,Blue—
can be added together to generate the other
colors.
At the center of the triangle is white.
The colors in the triangle can assigned
three coordinates, like a vector,
determined by how much red
or blue or green
is mixed to make that color.
For example,
a saturated red added to
a saturated green makes …yellow.
Red and green make YELLOW???
Yup.
We’ll show you how.

16. Maxwell’s Triangle Think of the saturated red and green colors
on Maxwell’s diagram as vectors.
Now, imagine “decomposing” these R and G
vectors into the sum of the dashed arrows.

17. Maxwell’s Triangle See how two of the decomposed vectors
that run along the right edge of the triangle
are co-linear but point in exactly opposite directions?
They cancel each other.
This leaves the shorter vectors components
these vectors have the same direction and
point from yellow.
They represent the yellow “product”
from adding red and green.

18. Maxwell’s Triangle
Blue + Yellow = White?!
Blue + yellow vectors
point in exactly opposite
direction and cancel to
make white.

20. In the early 1800’s,
Ogden Rood physicist
and
Michael-Eugene Chevreul chemist
ebxplored optical mixing.

22. CIE Chromaticity curve
Maxwell’s triangle excludes
some colors that are visible to eye.
The chromaticity diagram is meant to
show extra colors visible to the eye.
Pink at x=0.34, y= 0.23

23. A mid-tone flesh pink
Unsaturated, non-spectral hues are especially likely to be found as metameric mixtures.

24. Color wheels for mixing paint to neutralize color: OK.
yellow
green
red
cyan
magenta
Not OK for assigning visual compliment in
spectroscopic analysis of compounds !!
blue

27. blue + yellow = green One light beam!!!!
Subtractive color mixing: light colors are subtracted from one white light beam
blue + yellow = green
white light beam =
sum of all spectral colors
reflects
this much
spectrum
light
reflected
By both
blue paint
shining on:
reflects
Green
is only color reflected by both the blue and yellow paints.
All red, orange, yellow, blue, violet removed.
yellow paint
One light beam!!!!

28. A transmittance —or reflectance— spectrum reflects this much spectrum
ultramarine
light reflected by both
reflects
chrome yellow

29. blue + yellow = green One light beam!!!! white light beam =
sum of all spectral colors
This blue reflects no violet.
light
reflected
by both
blue paint
(cerulean)
shining on:
reflects
a brighter green, less dull, because the (violet + orange = brown) is absent
yellow paint
(lemon yellow)
This yellow reflects no orange.
One light beam!!!!

30. reflects this much spectrum Cerulean blue reflects lemon yellow
light reflected by both
reflects
lemon yellow

31. Light “hues” removed from one beam
So the primary colors are not Red-Yellow-Blue??!!
Primary Colors for Color Mixing
Additive
Multiple light beams added
Subtractive
Light “hues” removed from one beam
primary colors
Y-M-C
yellow/magenta/cyan
Y + M + C = Black
primary colors
R-G-B
red-blue-green
R + G + B = White
secondary colors
Y-M-C
secondary colors
R-B-G
Demonstrate this:
with 3 slide projectors
Demonstrate this:
with transparencies

32. (some) Color Terminology
common idea
scientific term
Hue green Lmax, nm or Do
what color is grass?
Saturation how intense the color, e, absorption coefficient
relative to grey
Luminosity relative brightness concentration
(Value) how much white/black is added (e.g., molarity)
Non-spectral hues are not in the rainbow! are not a component of white light
examples: are not due to one wavelength of light
brown, salmon, magenta, purple, pink

33. or saturation

34. How does all this relate to spectroscopy of transition metals complexes?

35. Conversion between the two primary color systems,
Red-Green-Blue and Cyan-Magenta-Yellow
illustrates the mathematical concept of equivalent basis sets
and their interconversion
Examples of changing 3-dimensional basis sets:
Color space: RGB CMY
Geometrical Space:
Cartesian Coordinates (x,y,z,) into Spherical (Polar) Coordinates (r, )
Chemical “Space”: Atomic orbitals and molecular orbitals

36. philosophy
art
math
history
COLOR
biology
chemistry
language

38. - Renoir

39. La Grenouillere - Claude Monet

40. Houses of Parlement - Claude Monet

41. La Grande Jatte - George Seurat

43. Parade - George Seurat

44. The Apple Pickers - Pisarro

45. The Apple Pickers - details - Pisarro

46. The Apple Pickers - details - Pisarro