class Color:
    __COLOR_VARIANTS = ['blue', 'red', 'green', 'black', 'white']

    def __init__(self, color):
        self.__color = color

    def set_color(self, new_color):
        new_color_lower = new_color.lower()
        if new_color_lower in [color.lower() for color in self.__COLOR_VARIANTS]:
            self.__color = new_color_lower
            print(f'Color changed to {new_color}')
        else:
            print(f'Cannot change color to {new_color}')

    def get_color(self):
        return self.__color

# Пример использования
my_color = Color('blue')
print(my_color.get_color())  # Output: blue

my_color.set_color('red')
print(my_color.get_color())  # Output: red

my_color.set_color('black')
print(my_color.get_color())  # Output: black

my_color.set_color('purple')  # Output: Cannot change color to purple
print(my_color.get_color())  # Output: black