Create Opaque sphere in pyqtgraph opengl

Question

I am able to use a mesh to create a transparent sphere like this in pyqtgraph opengl:

import pyqtgraph.opengl as gl
....
self.anim = gl.GLViewWidget()
sphere = gl.MeshData.sphere(rows=100, cols=100, radius=6378)
globe = gl.GLMeshItem(
    meshdata=sphere,
    smooth=True,
    color=(0, 0, 1, 1),
    shader="balloon",
    glOptions="additive",
)
self.anim.addItem(globe)

How can I make the sphere opaque so background objects are not visible?