code: def _get_color(self, age):
          
          if age == self.tree.age:
              return self.leaf_color
          color = self.stem_color
          tree = self.tree
  
          if len(color) == 3:
              return color
  
          diff = [color[i+3]-color[i] for i in range(3)]
          per_age = [diff[i]/(tree.age-1) for i in range(3)]
  
          return tuple([int(color[i]+per_age[i]*age) for i in range(3)])
docs: Get the fill color depending on age.
  
          Args:
              age (int): The age of the branch/es
  
          Returns:
              tuple: (r, g, b)