Color Transform Effect – https://github.com/vanruesc/postprocessing/issues/124

color_transform.frag

#define LUT_FLIP_Y
#pragma glslify: applyTransform = require('glsl-lut')

uniform sampler2D colorTransformLookup;

void mainImage(const in vec4 inputColor, const in vec2 uv, out vec4 outputColor) {
	outputColor = applyTransform(inputColor, colorTransformLookup);
}

ColorTransformEffect.js

import {
	NearestFilter,
	RGBAFormat,
	Uniform
} from 'three'

import {
	BlendFunction,
	Effect
} from 'postprocessing'

import fragment from 'color_transform.frag'

export class ColorTransformEffect extends Effect {
	constructor ({ lutTexture }) {
		super('ColorTransformEffect', fragment, {
			blendFunction: BlendFunction.NORMAL,
			uniforms: new Map([
				['colorTransformLookup', new Uniform(lutTexture)]
			])
		})

		lutTexture.magFilter = NearestFilter
		lutTexture.minFilter = NearestFilter
		lutTexture.format = RGBAFormat
		lutTexture.generateMipmaps = false
		lutTexture.needsUpdate = true
	}
}