If you want a transparent background in three.js, you need a pass in the alpha parameter to the WebGLRenderer constructors in the below-given code −
var renderer = new THREE.WebGLRenderer( {alpha: true } );
// You can leave the clear color at the defaultvalue.
renderer.setClearColor( 0x000000, 0 ); //defaultHowever, to set the background color,
renderer.setClearColor(0xb0f442 );