Purple is a secondary color that is made by mixing red and blue light or pigment. The exact ratio of red to blue that makes purple depends on the shade of purple you want to produce. Purple ranges from reddish purples to bluish purples, so the more red or blue you add, the more the purple will shift towards that primary color. Finding the right balance of red and blue to make the perfect purple for your needs requires some experimentation.
How the Eye Perceives Color
To understand how combining red and blue makes purple, it helps to first understand how we see color. The human eye has receptors called cones that detect different wavelengths of light. There are cones for red light, green light, and blue light. When all three types of cones are stimulated equally, we see white light. When only the red and blue cones are stimulated, and not the green, our brain perceives the color purple.
So by mixing red and blue, we can create the wavelengths of light that correspond to the color purple. The ratios needed to produce different purples depend on how much we want to stimulate the red or the blue cones relative to each other.
Pure Purple Hue
The “purest” shade of purple, with no tint of red or blue, is obtained with a ratio of approximately 2 parts red to 1 part blue. This stimulates the red and blue cones equally to give the hue that we recognize as vivid purple.
In paint pigments, a 2:1 red to blue ratio is approximated by mixing magenta (which has more red pigment) and cyan (which has more blue pigment). Magenta pigment reflects red and blue light while absorbing green light. Cyan pigment reflects blue and green light while absorbing red light. Combining these gives a pigment that reflects red and blue but not green – producing a vivid purple.
So for the purest purple hue in light or pigment, the ideal ratio is:
Red:Blue :: 2:1
Reddish Purples
If more red is added relative to the blue, it produces a purple with a strong reddish tint. The cones in our eyes detect more red wavelengths than blue.
Adding roughly 3 parts red pigment to 1 part blue pigment gives a reddish purple. In paint, this can be mixed by combining more magenta than cyan. In light, having more power in the red wavelengths compared to the blue creates a reddish purple.
Some examples of reddish purples include:
- Raspberry
- Magenta
- Mulberry
A general ratio for reddish purples is:
Red:Blue :: 3:1
Bluish Purples
On the other end of the spectrum, using more blue in the mix creates purples with a bluish tint. Having approximately 1 part red to 3 parts blue gives a bluish purple.
In paints, combining more cyan pigment than magenta pigment creates these cool-toned purples. In light, having more power in the blue wavelengths stimulates the blue color receptors more than the red.
Some examples of bluish purples include:
- Lavender
- Wisteria
- Lilac
The general ratio for bluish purples is:
Red:Blue :: 1:3
Ratios for Shades of Purple
Here is a summary of the approximate red to blue ratios that produce different shades of purple:
| Shade of Purple | Red : Blue Ratio |
|---|---|
| Vivid purple, no tint | 2:1 |
| Reddish purples | 3:1 |
| Bluish purples | 1:3 |
As mentioned earlier though, the exact ratios can vary depending on how saturated you want the color to be. A heavily reddish purple may be closer to 4:1 or 5:1 even. A strongly bluish purple could be 1:4 or 1:5. Finding the right balance comes down to experimenting and adjusting the amounts of red and blue until you achieve the perfect purple for your project.
Mixing Paint Pigments
When mixing purple paints, you’ll need to mix a red paint pigment with a blue one. Some common pigment options include:
Red pigments:
- Cadmium red
- Alizarin crimson
- Quinacridone magenta
Blue pigments:
- Ultramarine blue
- Cobalt blue
- Phthalo blue
Cadmium red and ultramarine blue are a classic combination for mixing vibrant purple. Alizarin crimson has a cool bluish red tone that also works well with the warmer ultramarine blue.
Phthalo blue is a very intense pigment, so only a small amount is needed to make deep vivid purples. Combine it sparingly with magenta shades like quinacridone to achieve saturated purple.
When mixing paints, it’s best to add small amounts of pigment at a time to slowly achieve the desired shade. Pre-mix the paints on a palette before applying to your canvas or paper. Test strips are helpful to compare subtle variations in purple tones. Keep track of recipe ratios that produce colors you like for consistent results.
Combining Light Wavelengths
To produce purple light, you need light sources that emit red and blue wavelengths. Red light has wavelengths around 700 nm, while blue light is around 450 nm.
Combining a red LED light (around 620-700 nm wavelengths) with a blue LED light (450-495 nm) will produce purple. Varying the intensities of the two lights will shift the tone. Having more intense red will appear reddish purple, while more intense blue gives a bluish purple.
Computer screens and TVs create purple by combining different amounts of power to the red and blue color channels. Removing the green channel stimulates just the red and blue color receptors in our eyes.
With stage lighting, colored gels or filters are used to create red and blue hues that mix to make purple. The gels can be continuously adjusted to change the purple tone and saturation.
Lasers are another light source that can be combined to produce purple by aiming a red and blue laser at the same spot. The color is controlled by adjusting the power output of each laser.
Pigment vs. Light Mixing
One difference between mixing pigments and mixing colored light is the resulting secondary colors:
| Primary Colors | Mixed Pigments | Mixed Light |
|---|---|---|
| Red + Blue | Purple | Magenta |
| Red + Green | Brown | Yellow |
| Green + Blue | Greenish brown | Cyan |
This comes down to the particle nature of pigments versus the waves of light. When pigments absorb certain wavelengths, the reflected blended color differs from pure additive light mixing.
So while combining red and blue pigment makes purple, combining red and blue light makes magenta. The same red/blue ratio principles apply in both cases. But for pure purple light, it may be better to mix laser sources or gels rather than LEDs.
Using Purple in Design
Purple has many applications in art, decor, fashion, and graphics. Here are some popular ways to utilize different purples:
- Vivid purples – Grab attention, energetic accents
- Light purples – Soft, feminine touches
- Pale purples – Ethereal, whimsical mood
- Dark purples – Elegant, rich backdrops
- Muted purples – Soothing, subtle neutrals
Reddish purples suggest passion, vibrancy, and intrigue. Bluish purples create calming, cool spaces. Adjust the purple shade to suit your unique needs.
Use the color wheel and the ratios described here to mix custom purples. Start with base primary paints or light filters, then experiment adding more red or blue to achieve your perfect purple tone.
Conclusion
Purple is formed by combining red and blue wavelengths of light or pigment particles. Adjusting the ratio of red to blue shifts the tone from vivid purple, to reddish purples, to bluish purples. A 2:1 red to blue ratio produces the purest purple hue. More red makes reddish purples, while more blue makes bluish purples. Mixing red and blue pigments makes a different shade of purple than combining red and blue light. But the same principles of color ratio apply. With some experimentation, you can create an endless range of purple tones for any design or decor need.