By default Vizard has a light source attached to the head position. So when you look in the mirror the head light is not facing the avatar. You should disable the head light and add a fixed light source. For example, the following code will create a directional light that point downward:
Code:
viz.MainView.getHeadLight().disable()
sunlight = viz.addLight()
sunlight.position(0,1,0,0)
sunlight.ambient([0.6]*3)
Also, try reducing the ambient light value. The values range from 0-1, so setting it to 3 will max out the ambient value and make everything look over bright.