In THREE.js, If two plane are orthogonal with each other, the transparent of one plane is wrong.
var material = new THREE.MeshBasicMaterial({
transparent: true,
side: THREE.DoubleSide,
fog: false,
color: 0x00FF00,
opacity: 0.3
});
If you add Three plane, the result is the same, there is no transparent effect in the first plane.
jsfiddle Code1