Colored fabric or wall behind subject — blue/green for chroma-key, white for bright studio portraits, black for contrast. Essential for post-production compositing.
You stand in front of a solid-colored surface and the backdrop disappears — or can be swapped out later in the edit. That's the core idea of backdrops. We use them to separate the subject from its environment, either during shooting or as preparation for post-production. The color dictates the strategy.
Green and Blue are your chroma key colors. Green is dominant because human skin contains fewer green pigments — separation is cleaner, with less fringe around the edges. We use blue when green is present in the subject itself (green eyes, clothing, plants). Lighting is critical: the backdrop must be lit absolutely evenly, without wrinkles, without hot spots. Any unevenness will become a problem later during keying. A poorly lit green screen will cost you two hours of rotoscoping work that could have been avoided. The distance between the subject and the backdrop should be at least 1.5 to 2 meters — this avoids color spill (green or blue light falling on the actor) and ensures a clean edge for the mask.
White is used for classic studio shots, especially for interviews or beauty shots. A white backdrop appears clean, professional, timeless — and reflects light, which you need to illuminate the subject itself brightly and with rich detail. Black is the opposite: maximum contrast, dramatic separation, depth. The actor or product stands against nothingness. However, black backdrops require lighting discipline — if your key light is too harsh, you'll lose detail in the shadows.
Practical Details: Material matters. Paper backdrops are inexpensive, wrinkle easily, and need constant smoothing. Fabric is more durable but harder to transport. For chroma key, you need specially treated fabrics (matte, non-reflective). Even small light reflections on green screens create casting errors in the keyer. You should control the lighting of the backdrop separately — don't just consider it a reflection of your key light. Often, you'll use dedicated backlight on the background to ensure uniformity.
Another point: You also need to consider the distance between the subject and the backdrop for depth of field. If you're shooting with a wide aperture (f/2.8 or wider), the backdrop can become out of focus — this is sometimes desired, sometimes undesired for later chroma key. Plan for this in advance.