Many people are familiar with the phenomenon that mixing blue and yellow paints or pigments together results in the color green. But why does this happen on a scientific level? The answer lies in the properties of light and how our eyes perceive different wavelengths of light as different colors. By understanding some basics about the science of color and light, we can explain why combining blue and yellow gives us green.
How Our Eyes See Color
To understand what’s happening when blue and yellow are mixed, we first need to take a step back and talk about how we see color at all. The process starts with light. Light visible to the human eye consists of a spectrum of different wavelengths, each corresponding to a different color. Within this visible spectrum, blue light has shorter wavelengths while yellow light has longer wavelengths.
When light enters our eye, it hits specialized receptor cells in the retina called cones. There are three types of cones, each sensitive to a different range of wavelengths – short, medium and long. Signals from the cones are sent to the brain which interprets the relative stimulation of the different cone types as different colors. For example, strong stimulation of the short wavelength cones accompanied by weaker stimulation of the medium and long cones is interpreted as the color blue.
Additive Color Mixing
So what happens when blue and yellow light enters the eye at the same time? The cones respond to the combined input of the short wavelengths from the blue light and longer wavelengths from the yellow light. This combination of stimulation is read by the brain as the color green!
This is called additive color mixing, as the wavelengths of light are being added together. Red, green and blue are the primary additive colors, meaning combinations of these three colors in different proportions can produce all other colors in the visible spectrum. Yellow is a secondary color made by combining red and green light. When blue light is added to yellow, which already contains red and green, the result is white light perceived as the color green.
Pigments and Subtractive Color Mixing
The same principle applies when mixing blue and yellow pigments or paints. Pigments work by absorbing some wavelengths of light and reflecting others. Yellow pigment absorbs the shorter blue and violet wavelengths while reflecting the longer green, yellow and red wavelengths. Blue pigment absorbs the longer yellow, orange and red wavelengths while reflecting the shorter blue and violet wavelengths.
When yellow and blue pigments are mixed together, both the shorter and longer wavelengths are absorbed. The predominantly reflected light contains medium wavelengths corresponding to green. This is called subtractive color mixing, as wavelengths are being subtracted through absorption by the pigments.
The Color Wheel
The relationship between blue, yellow and green is clearly demonstrated on the color wheel. This diagram illustrates how colors relate to one another based on their wavelengths and additive/subtractive mixing. Blue and yellow appear on opposite sides of the color wheel. Mixing opposites yields a color midway between them – in this case green.
| Color | Wavelength |
|---|---|
| Red | ~700 nm |
| Orange | ~610 nm |
| Yellow | ~580 nm |
| Green | ~510 nm |
| Blue | ~470 nm |
| Violet | ~420 nm |
Light and Pigment Interactions
An interesting intersection of additive and subtractive color mixing occurs when colored light shines on a pigment of a different color. For example, blue light shining on a yellow pigment will be absorbed, while the yellow pigment reflects back the longer green and red wavelengths – resulting in the perception of green where the two intersect.
This effect is well demonstrated in Claude Monet’s famous painting Impression, Sunrise, which depicts a red sun casting orange and blue light over the landscape and water. The interactions of the colored light with the water, buildings and air results in a vivid interplay of green, purple and yellow tones throughout the painting.
Understanding the dual nature of light and pigments is key to anticipating how colors will mix together and interact in different contexts.
Color Perception and the Brain
While we have focused on the physics of light and pigments, it’s important to note that color perception takes place in the brain. The receptors in our eyes simply detect different wavelengths of light – it’s up to the brain to interpret the signals as color. Factors like shadow, context and surrounding colors can influence which wavelengths are perceived as which colors.
Interestingly, a phenomenon called metamerism means that different combinations of wavelengths can sometimes be perceived as the same color. A mix of red and blue light might produce the same green color sensation as a mix of yellow and blue light, even though the wavelength combinations differ. Our brains can interpret different inputs as the same output color.
This complexity in color vision processing explains some of the subjective nature of color experience. Two people with normally functioning color vision can still perceive colors slightly differently!
Conclusion
When blue and yellow paint or light mix together, the resulting color is green. This is due to the additive mixing of blue’s short wavelengths and yellow’s longer wavelengths, or the subtractive absorption of violets and blues from the color spectrum by yellow and blue pigments respectively. Understanding the science behind how we see color helps explain the relationships between different hues predicted by color theory diagrams like the color wheel. Mixing blue and yellow always yields green – but our brains also play a role in how we perceive color, adding complexity to this visual process fundamental to human experience.