These work with all material types. First set the material's blending mode to THREE.CustomBlending, then set the desired Blending Equation, Source Factor and Destination Factor.
const material = new THREE.MeshBasicMaterial( {color: 0x00ff00} );
material.blending = THREE.CustomBlending;
material.blendEquation = THREE.AddEquation; //default
material.blendSrc = THREE.SrcAlphaFactor; //default
material.blendDst = THREE.OneMinusSrcAlphaFactor; //default
[example:webgl_materials_blending_custom materials / blending / custom ]
THREE.AddEquation
THREE.SubtractEquation
THREE.ReverseSubtractEquation
THREE.MinEquation
THREE.MaxEquation
THREE.ZeroFactor
THREE.OneFactor
THREE.SrcColorFactor
THREE.OneMinusSrcColorFactor
THREE.SrcAlphaFactor
THREE.OneMinusSrcAlphaFactor
THREE.DstAlphaFactor
THREE.OneMinusDstAlphaFactor
THREE.DstColorFactor
THREE.OneMinusDstColorFactor
THREE.SrcAlphaSaturateFactor
All of the Source Factors are valid as Destination Factors, except for THREE.SrcAlphaSaturateFactor
[link:https://github.com/mrdoob/three.js/blob/master/src/constants.js src/constants.js]