input: Write a python function to find dark colors (Black, Purple) from a given list.
  assert find_dark_colors(['Red', 'Orange', 'Green', 'Purple', 'Black', 'White']) == ['Purple', 'Black']
  assert find_dark_colors(['Yellow', 'Blue', 'Purple']) == ['Purple']
  assert find_dark_colors(['Pink', 'White', 'Black']) == ['Black']
output: def find_dark_colors(colors):
      dark_colors = ['Black', 'Purple']
      return [color for color in colors if color in dark_colors]