three.js/examples/js/shaders/ColorifyShader.js

/**
 * Colorify shader
 */

THREE.ColorifyShader = {

	uniforms: {

		"tDiffuse": { value: null },
		"color": { value: new THREE.Color( 0xffffff ) }

	},

	vertexShader: [

		"varying vec2 vUv;",

		"void main() {",

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

		"}"

	].join( "\n" ),

	fragmentShader: [

		"uniform vec3 color;",
		"uniform sampler2D tDiffuse;",

		"varying vec2 vUv;",

		"void main() {",

		"	vec4 texel = texture2D( tDiffuse, vUv );",

		"	vec3 luma = vec3( 0.299, 0.587, 0.114 );",
		"	float v = dot( texel.xyz, luma );",

		"	gl_FragColor = vec4( v * color, texel.w );",

		"}"

	].join( "\n" )

};