The powers of an HOA are generally controlled by the declaration of covenants/CC&Rs. Typically, the HOA has the power to maintain the common areas of the property, which includes the exterior of a condominium complex. If the CC&Rs require that homeowner approval for the painting change is required, then the HOA's independent action would be unlawful, and you could sue the board to force them to repaint the property.
However, if the HOA provides for an Architectural Control Committee (ACC), or similar language in the CC&Rs, then the board could make a rule concerning paint color, and the only requirements would be that the proposed rule would have to be put on an agenda, so that members could come and object to the color change. After that, it would be up to the HOA to decide whether or not to make the change.
As you can see, there was a specific reason why I wanted to review the CC&Rs of your community. You can, of course, review them yourself, based on the information that I've provided, and then determine if the HOA's actions are lawful.
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