Android : ImmediateModeRenderer20 can't set alpha

I can't seems to get alpha to work when I draw strips with the following code, its always solid black. Did I miss something?

gl20 = new ImmediateModeRenderer20(false, true, 1);

Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
Gdx.gl.glEnable(GL20.GL_BLEND);
Gdx.gl.glBlendFunc(GL20.GL_SRC_ALPHA, GL20.GL_ONE_MINUS_SRC_ALPHA);

gl20.begin(cam.combined, GL20.GL_TRIANGLE_STRIP);
gl20.color(color.r, color.g, color.b, color.a); // color.a is .5f
gl20.texCoord(tc.x, 0f);
gl20.vertex(point.x, point.y, 0f);
gl20.end();