Monochrome backing for chroma-key compositing—preferred over green because blue wavelength doesn't interfere with skin tones. Even lighting and separation distance are critical.
The blue background replaces green because its wavelength falls outside the range of human skin tones. This sounds simple, but it's crucial on set: you're working with a color that naturally occurs less frequently in costumes, props, or makeup. Greenscreen was the standard for a long time—cheap, bright, efficient. But any actor with a green sweater or blond hair (which reflects yellowish-green) means masking headaches in post-production. Bluescreen elegantly bypasses this.
In practice, this means you set up a blue fabric or a painted wall, light it completely evenly—this is the critical point—and place your talent at least 1.5 to 2 meters in front of it. Why this distance? Because otherwise, the camera will capture spill: the reflected blue bouncing back from the background onto the face and costume. Spill equals keying trouble. The lighting of the screen must be uniform, no hot spots, no gradients. A variation of just 5-10% in brightness creates problems for yourself when the keyer (your VFX supervisor or the software) starts to compensate.
On-Set Technique: Use LED panels or softboxes, not spotlights. RGB LEDs can even be precisely tuned to the correct blue wavelength (between 450 and 500 nm)—some studios swear by this. The camera itself is secondary: bluescreen works with Red, Alexa, even with good consumer equipment. More important is the codec—ProRes or DNxHD give you more freedom in editing than compressed H.264.
In post-production, you then apply your keyer—whether Nuke, After Effects, or DaVinci. Bluescreen provides more information for the algorithm here than greenscreen because the chroma channels interfere less with luma. This means cleaner edges, especially around hair. Some projects also use a combination: bluescreen for close-ups and talent, greenscreen for larger sets or background production—because green is simply brighter and absorbs less light.
Beware of cheap blue screens from online retailers: the color is often not saturated enough or too dark blue. Editing will become a Sisyphean task. Invest in a professional screen or have one custom-painted—it pays off immediately.