Changing one colour with hue curves and secondaries

Primary correction changes the whole picture. Sometimes you want to change one colour only: a sky that should be bluer, a shirt that is too loud, grass that looks yellow, or skin that has picked up a green cast from nearby leaves. Video by Zaweba has two kinds of tool for that, hue curves and a secondary key, and between them they handle most selective colour work.

The five hue curves

These curves don't map brightness to brightness. Along the bottom of each is a property of the pixels, and the curve changes another property for them.

Hue vs saturation is the one you will use most. The bottom of the curve runs round the colour wheel. Pull it down at blue and blue things lose saturation; push it up at orange and orange things become richer. Calming a bright red jacket without touching the face next to it takes one point.

Hue vs hue shifts one colour towards a neighbour. Yellowish grass can be moved towards green, or a teal sky nudged towards a cleaner blue. Hue vs brightness darkens or lightens a chosen colour, which is the classic way to deepen a blue sky so it doesn't look washed out.

Brightness vs saturation changes saturation by tone. It is good for pulling colour out of the deepest shadows, where cameras often produce noisy, coloured blotches, or out of the brightest highlights. Saturation vs saturation changes how saturated already saturated parts are, so you can tame the loudest colours while lifting quieter ones.

The secondary key

When curves are too broad, use the secondary key. You pick a range of hue, saturation and brightness, and the key selects only pixels within it. That selection then gets its own hue, saturation and brightness change.

The key view is what makes it practical. Switch it on and the viewer shows what is selected, so you can see whether you caught the whole sky or also grabbed a blue car. Widen or narrow each range until the selection is clean, then switch back to the normal picture and make the change.

Skin is the most common target. Select the skin tones, then shift the hue slightly or lower the saturation, and faces look healthier while the rest of the frame stays exactly as it was.

When to use which

Hue curves are quick and global. They change a colour everywhere in the shot, which is fine when there is only one blue thing in frame. The secondary key is more precise because it also considers brightness and saturation, so a light blue sky can be separated from a dark blue coat.

If you need to limit a change to part of the frame as well as one colour, combine it with a mask. The masks in Video by Zaweba can be keyframed and tracked, so a selection can follow a moving subject.

Mistakes that give it away

Selective changes are easy to overdo. Pushing a colour far from its neighbours makes edges look cut out, and a sky suddenly much darker than the horizon line looks false. Move in small steps and check the whole frame, not just the bit you are changing.

Noise is the other trap. Cheaper cameras and AI-generated clips often have soft, noisy colour, and a tight key will flicker on and off from frame to frame. Soften the key by widening its ranges a little and play the shot through before you move on.

Lastly, do primary correction first. If white balance is off, every colour is in the wrong place and the key has to work much harder. Fix the basics with the main colour controls, then come here for the detail.

Used with care, these tools let Video by Zaweba change a single colour so naturally that nobody watching would know it was ever different.