What you'll need
Duotones look best when the highlights and shadows in your source clip are exaggerated or starkly different. Starting in the Effects workspace (Window > Workspaces > Effects), expand the Lumetri Color panel. In the Basic Correction section, click Auto to quickly balance the contrast, highlights, and shadows. Adjust the Tone sliders individually, if necessary, to finesse the look.
Create an adjustment layer (File > New > Adjustment Layer) and add it to the sequence. Expand the Effects panel and apply the Tint effect to it. Your clip will look black and white. In the Effect Controls panel, set Map Black and Map White to your duotone colors. For naturalistic results, make the “black” color darker than the “white” color.
Sticking with the naturalistic look, you can expand the tonal range by adding another adjustment layer above the other clips and applying the Ramp effect to it with an Opacity blend mode of Overlay. To complete the look, choose a Linear Ramp shape, leave the default colors, and blend it halfway with the original.
From here, you could animate the duotone effect by keyframing the mapped colors or its amount over time.
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