It can be seen that the subject of the portrait in this photo has only one main tone, while the shadow behind presents different colors. How to create this effect?

You may remember the "chromatic dispersion" experiment you did in your elementary school science class (or your junior high school physics class), in which sunlight is refracted through a prism to form a "rainbow" because what "white" sunlight is actually a combination of many different monochromatic light with different wavelengths. On the other hand, multiple monochromatic lights can be combined into a single color composite light under a certain conditions.

In photography, the light emitted by the photographic lamp and flash is not actually monochromatic light in the optical sense (which cannot be decomposed again), but "composite light of a single color", which is also "synthesized" by the light of different colors.
Speaking of the "synthesis" of colors, we have to mention the trichromatic theory. The three primary colors of light are red, green, and blue. This is because these three kinds of cones in the human eye that are responsible for color perception are the most sensitive to red, green, and blue rays, and these three kinds of light cannot be formed by adding up other colors of light, but these three kinds of light can be added up to form other colors of light.
Based on the above principle, we can artificially simulate three primary colors of light, shining the light on the character from different angles. Since the character is exposed to three colors of light, red, green, and blue will eventually overlay white, which is the "normal" in photography.

Color filter is a type of photographic prop made of gelatin and used to change the light colors.

These three lights have been installed with different color filter. Red, green and blue lights are placed in different places, so are the shadow colors behind the characters. You can change them around for a more interesting shot.

To make a clearer silhouette in the background, we can also use the standard cover of the outshot light or the bare light of the hot boot flash without any soft light accessories such as a softbox or soft umbrella.
If you find that the colorful shadow on the background is not clear, it is probably because the subject is far away from the background. The solution is to get the subject as close to the background as possible, so that the silhouette of the shadow would be clearer and more visible.
Here, I recommend the QIAYA flash with a variety of color filters to help you make your interesting shots.

12 SMD CRI 95+ LED Bulb Mini Pocket-Size On-Camera LED Video Light

QIAYA SL-12 is a pocket sized LED fill light. It is incredibly compact and lightweight with 12 SMD LED bulbs that are powerful in the palm of your hand. Illuminance ranges from 0.5m 660Lux to 1m 165Lux.
9 dimming levels and superb lighting effect can perfectly meet your shooting needs.
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