three.js/examples/js/shaders/HueSaturationShader.js

/**
 * Hue and saturation adjustment
 * https://github.com/evanw/glfx.js
 * hue: -1 to 1 (-1 is 180 degrees in the negative direction, 0 is no change, etc.
 * saturation: -1 to 1 (-1 is solid gray, 0 is no change, and 1 is maximum contrast)
 */

THREE.HueSaturationShader = {

	uniforms: {

		"tDiffuse": { value: null },
		"hue": { value: 0 },
		"saturation": { value: 0 }

	},

	vertexShader: [

		"varying vec2 vUv;",

		"void main() {",

		"	vUv = uv;",

		"	gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",

		"}"

	].join( "\n" ),

	fragmentShader: [

		"uniform sampler2D tDiffuse;",
		"uniform float hue;",
		"uniform float saturation;",

		"varying vec2 vUv;",

		"void main() {",

		"	gl_FragColor = texture2D( tDiffuse, vUv );",

		// hue
		"	float angle = hue * 3.14159265;",
		"	float s = sin(angle), c = cos(angle);",
		"	vec3 weights = (vec3(2.0 * c, -sqrt(3.0) * s - c, sqrt(3.0) * s - c) + 1.0) / 3.0;",
		"	float len = length(gl_FragColor.rgb);",
		"	gl_FragColor.rgb = vec3(",
		"		dot(gl_FragColor.rgb, weights.xyz),",
		"		dot(gl_FragColor.rgb, weights.zxy),",
		"		dot(gl_FragColor.rgb, weights.yzx)",
		"	);",

		// saturation
		"	float average = (gl_FragColor.r + gl_FragColor.g + gl_FragColor.b) / 3.0;",
		"	if (saturation > 0.0) {",
		"		gl_FragColor.rgb += (average - gl_FragColor.rgb) * (1.0 - 1.0 / (1.001 - saturation));",
		"	} else {",
		"		gl_FragColor.rgb += (average - gl_FragColor.rgb) * (-saturation);",
		"	}",

		"}"

	].join( "\n" )

};