The balance condition of a control surface is often determined by observing what aspect of the surface?

The balance condition of a control surface is primarily indicated by observing trailing edge movement. This aspect is crucial because the trailing edge's position can significantly affect the aerodynamic forces acting on the control surface. When a control surface, such as an aileron or elevator, is properly balanced, the trailing edge will move freely when subjected to aerodynamic loads without any assistance from the pilot or any additional force.

The other options, while they may hold some relevance in specific contexts, do not accurately reflect how balance is assessed. For instance, color change and surface texture do not directly provide information on how well the control surface responds to aerodynamic forces or how well it maintains equilibrium. Weight distribution is related to the overall aircraft balance but does not directly inform on the balance of the individual control surfaces themselves. Trailing edge movement gives a clear indication of how effectively the control surface is operating and can signal whether adjustments are needed to ensure optimal performance.