Pixi.Mesh gl_FragColor Alpha Channel

Hi,

I've tried to change the Alpha Channel on gl_FragColor on a Mesh, but it doesn't show a result as I expect.

For example, on the pixijs.io example ( https://pixijs.io/examples/#/mesh/triangle-color.js )

void main() {
        gl_FragColor = vec4(vColor, 1.0);
    }

If we changed the line into

void main() {
        gl_FragColor = vec4(vColor, 0.5);
    }

It doesn't show any difference. Is there any workaround/settings I need to adjust to use the alpha channel correctly?

Thanks.