Green skin. Green whites. A cast that survives every white balance preset you try. This is the single most common colour problem in interior video, and it happens because the control you are reaching for is the wrong axis.
Why Kelvin will never fix it
White balance has two independent axes:
- Kelvin moves the image orange to blue.
- Tint moves the image green to magenta.
A green cast lives entirely on the second one. You can sweep the Kelvin slider from 2000K to 10000K and watch the image go from orange to blue while staying just as green the whole way. There is no value that removes it, because green is not on that axis at all.
The full explanation of the two axes is here. For now: if a neutral object in your frame reads green while the warm/cool balance looks about right, stop touching Kelvin.
What is actually causing it
Nearly always one of these:
Fluorescent tubes. A fluorescent works by exciting phosphor with UV. The phosphor emits in narrow spikes rather than a smooth spectrum, and the strongest spike sits in the green region around 545 nm. Older and cheaper tubes are worse.
Inexpensive white LEDs. A white LED is usually a blue emitter with a phosphor coating filling in the rest. The fill is uneven: strong through green and yellow, weak in deep red. That is also why an LED can score a respectable CRI and still render a red jumper as brown.
Sodium and mercury vapour street lights. Extreme cases. Mercury vapour in particular is aggressively green and effectively uncorrectable.
A bi-colour panel with its tint dial off zero. Easy to knock and easy to miss.
Bounce off a green surface. Foliage outside a window, a painted wall, a grass field. The light was neutral before it hit the surface.
Diagnose it in thirty seconds
Turn the lights off one at a time and watch the monitor. The offender is usually obvious as soon as it goes dark.
If several sources are on and you cannot kill them individually, meter each one instead. Point a Kelvin and tint meter at each source in turn and note both numbers. A source reading a large green tint value is your problem, even if its Kelvin looks fine.
Do not try to judge this by eye. Chromatic adaptation means your visual system discounts a consistent cast within a few seconds of walking into the room. The camera has no such mechanism. That gap is precisely why footage looks worse than the room did.
Fix it at the light - the good option
Correcting the source fixes it for every camera pointed at the scene, and it means you are not spending dynamic range on a correction later.
| Gel | Use when |
|---|---|
| Full Minus Green | Older fluorescent tubes, strong cast |
| 1/2 Minus Green | Cheap LED panels, modern tubes |
| 1/4 Minus Green | Good LEDs that still skew a little |
| 1/8 Minus Green | Final match between two nearly-identical sources |
A Minus Green gel looks magenta - the name says what it takes out of the light, not what colour the sheet is. It is sometimes catalogued as 3308.
Other options at the source:
- Swap the bulbs. For a scene shot over several days, buying six matched high-CRI bulbs is cheaper than gelling and re-gelling.
- Dial magenta on a bi-colour panel. Most modern panels have a green/magenta control alongside the Kelvin one.
- Turn it off and light it yourself. Frequently the fastest answer for the overhead tubes in an office.
Fix it in the camera - the fast option
If you cannot reach the light, put the correction in the body.
- Meter the dominant source and note the tint value.
- Find the camera’s tint field: CC on Canon and ARRI, G/M on Sony, the A-B / G-M grid on Nikon and Fujifilm, Tint on Blackmagic.
- Dial magenta until a grey card reads neutral on a scope.
Watch the sign. Positive means green on most camera bodies and magenta in Resolve and Lightroom, so a value copied straight from the grade into the camera doubles the error instead of removing it.
Most stills bodies expose no tint field at all. In that case, note the number and fix it in the grade - but shoot a grey card first so the colourist has a reference.
Fix it in post - the last option
Lightroom or Camera Raw. Use the white balance eyedropper on something genuinely neutral: grey card, white shirt in the same light, a sheet of paper. It sets Kelvin and Tint together and gets you far closer than dragging sliders.
DaVinci Resolve. Temp and Tint in the primaries work on log and RAW. For a cast confined to part of the frame - the classic being fluorescent tubes behind a correctly lit subject - use a qualifier or a power window. A global correction fixes the background and pushes the subject magenta.
What post cannot fix:
- A clipped green channel. Once a channel hits the ceiling the information is gone.
- Green spill on a greenscreen shoot. It has already contaminated the matte.
- Mixed casts across a cut. If every take drifted differently, you are matching shots one at a time.
The workflow that stops it recurring
- Meter the key light for both Kelvin and tint before you roll.
- Correct at the source where you can reach it; in the camera where you cannot.
- Shoot a grey card at the head of every setup.
- Check a scope, not your eyes.
- Lock white balance. Auto WB drifting between takes turns one correction into forty.
Reading tint is the part most people skip, because most meters and every camera preset only give you Kelvin. KEV reports the magenta/green value alongside Kelvin on iPhone and iPad, which is what tells you how much to gel before you start guessing.