1You can pass the argument activefill when creating your rectangle.
2
3From effboot.org:
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5Fill color to use when the mouse pointer is moved over the item, if different from fill.
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7To do so, replace:
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9rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red')
10By:
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12rectangle = self.canvas.create_rectangle(x, y, x + 50, y + 50, fill='red', activefill='cyan')