1. 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. It’s not simple. It’s not real. It’s not universal.

2. 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: If the electromagnetic spectrum were a piano keyboard….. cosmic gamma X-rays UV Vis IR Radio induction power wavelength, nm 10 -8 10 -6 10 -4 10 -2 1 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 nm frequency, Hz 10 26 10 24 10 22 10 20 10 18 10 16 10 14 10 12 10 10 10 8 10 6 10 4 10 2 Hz the visible spectral region would be just one key!

3. 500600700750650550450400 Each of the “colors” of visible light has a corresponding wavelength between 400 to 700 nanometers (or nm). 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. 565 nm Light having a wavelength of near 565 nm will look yellow to most people.

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

5. 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. Beauty in the eye of the beholder.2

6. “What about red-orange?”, you say. “Red-orange light would also simultaneously stimulate the Red and Green receptors. See?” Beauty in the eye of the beholder.3 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.

7. When the R receptor gets about the same signal as the G receptor, or R = G, yellow is perceived. Beauty in the eye of the beholder.4 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.

9. THIS IS NOT YELLOW Magenta is not a real color. BiologyPhilosophy

10. Magenta is a non-spectral hue.

11. 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.

12. 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.

13. 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.

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

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

18. 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 CIE Chromaticity curve

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

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

23. ultramarine chrome yellow reflects this much spectrum reflects light reflected by both

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

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

26. venetian red viridian prussian blue “Mixing an intense paint with its hue complement is just adding reflectance to the dark parts of the spectrum, which flattens out the overall reflectance profile. So a reasonable first rule would be that unsaturated colors have flat reflectance curves. Unsaturated colors are closer to white, gray, or black, and these are all colors that have a flat reflectance profile (they only vary in the average height, or luminosity, of the profile).” www.handprint.com

27. 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 R-G-B red-blue-green R + G + B = White primary colors Y-M-C yellow/magenta/cyan Y + M + C = Black secondary colors Y-M-C secondary colors R-B-G Demonstrate this: with 3 slide projectors Demonstrate this: with transparencies

28. (some) Color Terminology Hue green  max, nm or  o what color is grass? Saturationhow intense the color, , 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 termcommon ideascientific term

29. or saturation

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

31. Metameric Colors Refuting the Physicalism of Color and bird nesting behavior!

32. Impression, Sunrise - Claude Monet

35. - Renoir

36. La Grenouillere - Claude Monet

38. Houses of Parlement - Claude Monet

41. Gare Saint Lazare - Claude Monet

44. La Grande Jatte - George Seurat

48. Parade - George Seurat

49. The Apple Pickers - Pisarro

50. The Apple Pickers - details - Pisarro

52. There is so much more… See: www.handprint.com