Change background color of NSButton

Assuming everything is hooked up in IB for your borderless button.

// *.h file
IBOutlet NSButton* myButton;

// *.m file
[[myButton cell] setBackgroundColor:[NSColor redColor]];

Note from the setBackgroundColor documentation:

“The background color is used only when drawing borderless buttons.”

If this won’t do it for you then you’ll need to override NSButton and implement the drawing yourself.

Good Luck.